Looking at a '72 Valiant...what do these cars weigh, or what does your combo weigh?
One thing to remember: Valiants are on a 108" WB, Darts are 111", so a 2nd gen Valiant (or Barracuda) is always lighter than a Dart. I'm not sure where Dusters fit into this.
I guess when you say Barracudas, you mean Notchies?
I'm also of the opinion that Plymouths are lighter than Dodges, and 108s are lighter than 111s.
Somehow,I think the Duster/Demons are about the lightest, along with the Scamps/Valiants/and probably the Nochies;with the 67 to 69 Darts coming in a very, very,close second; the fold down seat cars excepted.You just can't fit much of a tire on a Dart.The later, more "mature"Darts can be lightened up a tad by swapping out those tank bumpers. 2nd gen Barracuda bumpers are about the lightest.I think mine are about 30 pounds per end with brackets and bumperettes.
In about 71,my 70 Swinger340-4spd-8.75,factory stock, scaled at 3310(me in it).Well not quite stock; I think I was running G60-14 Polyglass GTs. Deducting my skinny *** 130pounds at the time,that makes 3180 with a half a tank.Adding a very generous 20 for the Gs and the Mags and the oo-oo 8track player with 4x 30watt speaker system ....................call it 3200
Similarly equipped, my 68 Formulas fastback car is ..............3464.But it has lots of aluminum; intake,heads,wheels,&4pd.Plus,it has lightweight front seats,headers,3" duals, and the GV.The aluminum parts advantage gets eaten up by the GV and pipes, to about a wash.I shelved the rear seat,34# so I'm at ..........3400 car only.That's 200 over the Swinger.
So; in comparison,2nd gen Fastback Barracudas are tanks!
I chose my tank, on account of the huge rear wheel houses and the heavier rear half.Then I lightened up the front as much as possible,yet keeping the very heavy p/s and booster.The full aluminum case tranny offsets the GearVendor.The battery went into the trunk. The aluminum wheels weigh half what an equivalent steel wheel weighs.But I tell you that 3" dual system with twin Dynomaxers is HEAVY at 72pounds.I got the rear weight bias to about 48%.
The p/s-p/b are staying.Don't even go there.That's why I built a real small block.(Sorry teenerboys),lol.