75 Duster vs 71-72
The rear bumper alone weighs about 88 lbs. That's the bumper, core, and shock mount brackets. At least that's what my '74's weighed. The non-shock '70-'72 bumpers without a crash core weigh about 1/3 that? Figure about 50 lbs extra. A '75 would have front and rear shock mounted bumpers, so just the bumpers by themselves would easily add over 100 lbs compared to '70-'72 bumpers. And the front's probably add more than the rears, my '74 didn't have a shock mounted front though so I don't have those weights.
There were also reinforcements added to the doors, a crash bar in the middle. I think that started in '74. My '74 has them at least. That adds a decent chunk of weight to the doors, it wasn't a couple lbs it was more like 10. You can tell the difference picking up a '70-73 door vs the '74, there were changes to all the window lift hardware as well which may have been part of it too. Then there was the extra electronic stuff, the smog stuff, etc. Adds up quick.
Some of the horsepower changes weren't just detuning either, there was a change in how the horsepower output was calculated. I think that was '73, I may be off by a year. The important part was that the biggest horsepower change year was also a change in the way the rating was done, the earlier ratings were without accessories, the later ones were with. So there was a decrease by all the belt driven stuff before any actual tuning changes. Although the compression ratio was lowered.
I dunno about "very little", it's a lot more than just the "basic shape". The entire chassis is basically identical, only a couple of captured nut changes in the frame rails for the bumpers. All of the structural stuff was the same, minor changes to the quarters for the side markers (72+) and bumper lip change (74+). Roof skin was the same, rockers, etc. Floor got the bump for the catalytic convertor in '75, inner driver's side bucket seat track changed because of that, small change to the sheet metal for the 4 speed hump because of the bump for the cat. Minor changes here and there, passenger front inner fender got a "dent" for the charcoal canister, some hole location differences. Heater box changed (in '73) so resulting firewall hole changes.
The were changes to the engine mounts (spool type for 73+), the sway bar and tab locations on the LCA's. And the K changed to route the sway bar through the middle like the E's had already done. '73+ UCA's were the large ball joint style, disk brakes changed to use larger wheel bearings and single piston calipers. Drum brakes changed too, spindles took the large upper ball joints and the outer wheel bearings were larger but the drum/drum cars stayed SBP. But torsion bars and springs were the same, non sway bar LCA's were the same.
Power steering boxes went large sector, manuals were unchanged. Pitman, idler and center links changed, the tapers pointed down instead of up.
A lot of the differences aren't substantial in my book. Like, you can still bolt most of the parts on. They won't be "correct" for the given year, but they still fit. All the suspension parts swap out, lots of people upgrade the UCA's, spindles and brakes. Doors can be changed out as a whole. Same for the entire front clip sheet metal, minus the captured nuts for the bumper brackets. Like it's not that hard to make a '74 look like a '71, for example. If you nit pick, sure, you can tell some things are from a '74. But it's not like trying to bolt E-body parts on an A-body or something.
I guess it's perspective, if you're trying to be year correct there's a lot of minor changes. If you're trying to say, clone a '74 to look like a '71, well, the majority of the parts just bolt on.
The rear bumper alone weighs about 88 lbs. That's the bumper, core, and shock mount brackets. At least that's what my '74's weighed. The non-shock '70-'72 bumpers without a crash core weigh about 1/3 that? Figure about 50 lbs extra. A '75 would have front and rear shock mounted bumpers, so just the bumpers by themselves would easily add over 100 lbs compared to '70-'72 bumpers. And the front's probably add more than the rears, my '74 didn't have a shock mounted front though so I don't have those weights.
There were also reinforcements added to the doors, a crash bar in the middle. I think that started in '74. My '74 has them at least. That adds a decent chunk of weight to the doors, it wasn't a couple lbs it was more like 10. You can tell the difference picking up a '70-73 door vs the '74, there were changes to all the window lift hardware as well which may have been part of it too. Then there was the extra electronic stuff, the smog stuff, etc. Adds up quick.
Some of the horsepower changes weren't just detuning either, there was a change in how the horsepower output was calculated. I think that was '73, I may be off by a year. The important part was that the biggest horsepower change year was also a change in the way the rating was done, the earlier ratings were without accessories, the later ones were with. So there was a decrease by all the belt driven stuff before any actual tuning changes. Although the compression ratio was lowered.
I dunno about "very little", it's a lot more than just the "basic shape". The entire chassis is basically identical, only a couple of captured nut changes in the frame rails for the bumpers. All of the structural stuff was the same, minor changes to the quarters for the side markers (72+) and bumper lip change (74+). Roof skin was the same, rockers, etc. Floor got the bump for the catalytic convertor in '75, inner driver's side bucket seat track changed because of that, small change to the sheet metal for the 4 speed hump because of the bump for the cat. Minor changes here and there, passenger front inner fender got a "dent" for the charcoal canister, some hole location differences. Heater box changed (in '73) so resulting firewall hole changes.
The were changes to the engine mounts (spool type for 73+), the sway bar and tab locations on the LCA's. And the K changed to route the sway bar through the middle like the E's had already done. '73+ UCA's were the large ball joint style, disk brakes changed to use larger wheel bearings and single piston calipers. Drum brakes changed too, spindles took the large upper ball joints and the outer wheel bearings were larger but the drum/drum cars stayed SBP. But torsion bars and springs were the same, non sway bar LCA's were the same.
Power steering boxes went large sector, manuals were unchanged. Pitman, idler and center links changed, the tapers pointed down instead of up.
A lot of the differences aren't substantial in my book. Like, you can still bolt most of the parts on. They won't be "correct" for the given year, but they still fit. All the suspension parts swap out, lots of people upgrade the UCA's, spindles and brakes. Doors can be changed out as a whole. Same for the entire front clip sheet metal, minus the captured nuts for the bumper brackets. Like it's not that hard to make a '74 look like a '71, for example. If you nit pick, sure, you can tell some things are from a '74. But it's not like trying to bolt E-body parts on an A-body or something.
I guess it's perspective, if you're trying to be year correct there's a lot of minor changes. If you're trying to say, clone a '74 to look like a '71, well, the majority of the parts just bolt on.