I'm Cummins swapping a '74 Duster, thought I'd share the progress.
I'm not really sure what you've been thinking about while planning this for 3-4 years but frankly you should have come to the conclusion pretty quickly that an 1,100 + lb engine in an A body is not a good idea. You can theorize/rationalize/explain this all you want but it's just not a reasonable endeavor. What is your vision for this thing besides just "doing something different?" If you're after tons of torque put a stroked 400 in it with stealth heads. It will weigh nearly the same as an iron head small block. If you're after the turbo, put a 360 in it with manifolds and go in the 9s. I'll put you in touch with a guy who can tell you how to do that.
A '73-up Duster weighs 3,400+lbs with a small block but it's going to be over 4,500 lbs when you're finished. Putting a Dana in it will add an extra 100 lbs to that. These cars were never meant to be that heavy, the chassis is not robust enough to handle that kind of mass. Again, a Duster is a "compact" passenger car, not a heavy duty vehicle with a rigid, traditional frame.
Not only that, as has been mentioned already, the front/rear weight bias of these cars is not so great to begin with. By doubling the engine weight over the nose and adding more support, it's going to be more like 75/25. Additionally, a 6BT is a really tall engine so the center of gravity is going to be much higher than it should be. You can probably forget about a hood too.
Just so you're aware, a 29" radiator is not fitting in an A body. Standard width is 22". With a 28" radiator half of it will be behind the radiator support panels with no air flow. Or are you cutting the radiator support out too?
That giant Mercedes truck trans is not fitting in that chassis without major alterations either so you're going to be cutting apart major structural sections of the car without any real sound engineering behind it. Forget that the chassis is also 50+ years old and probably fatigued from years of use and abuse. Understand that guys can barely fit a Tremec in these cars without major surgery so don't think you're just going to cut a little here or there and drop it in like it was meant to be.
Got a chassis jig to keep things straight when you start cutting and welding? If you're not a skilled fabricator or work in a body shop with pro-level equipment (does not sound like it), you're going to be in over your head. All that cutting and welding will put a bunch of heat into the metal, it's never going to be straight. It will also work harden when it flexes making it brittle and prone to cracking. You'd be better off having someone put a tube frame in it and work from there instead of modifying the original chassis beyond what's reasonable.
I'm not saying that you can't do this dude, I'm saying that you shouldn't. It's a misguided idea at best and will not be safe. Save the diesel for a truck where it belongs.
With all of the research I've done and all of the considerations and planning up to this point that I've done, I have most definitely come to the conclusion that this is a bad idea and incredibly stupid, but there's only so much planning that can be done before actually attempting to put things in motion. that's the nature of building and modifying cars. Great things often come from dumb ideas.
Ultimately with this car, I'm just trying to build something unique and not boring. I also just fell in love with diesel engines the more I learned about them in school. You don't see many diesel powered muscle cars (for good reason) but that's all the more reason to do it, I'm also just trying to show people that diesels aren't just for trucks, you can make genuinely fun and fast diesel powered cars (which is kind of the point of the YouTube channel as well)
when's the last time you were genuinely impressed with a turbo V8 build of a car?
For me it was probably the 5th or 6th time seeing one, after that it was just kind of boring.
I am aware that the 29 inch radiator won't fit with the stock core support, I'd prefer not to just cut up the one in the car, so I'll end up fabbing a core support.
I know the transmission is huge, I know the chassis is old and tired, is there sound engineering behind any of this? No, I'm just a Generator Technician with an incredibly dumb idea. I know this is going to be an incredible amount of work and there are most definitely skills I don't have that I will need with this project, so I'll learn as I go.
A tube chassis would probably be the best way to go about this, I agree. I also agree what I'm doing is unreasonable and it's a misguided idea at best, and I most definitely shouldn't proceed with this project, but I have a vision for the car and until I hit a point where it's full stop, nothing is going to work. I'm going to proceed and attempt to build this car, I mean what's the worst case scenario? I weld all of the sheet metal I've cut to figure out placement of the engine and trans back in, swap to a tubular kmember and throw a V8 back in it?
There is thought behind all of this and I'm not just going to blindly be cutting and welding. I'm going to save what I remove and do the best I can to ensure my car wont be ruined. I've owned it since 2016 and I love it, even though the stock drivetrain that was in it was in terrible shape and it barely ran as is.