Will a 350 Chevy fit into a 1972 dodge dart
What would get me the biggest bang for my buck if I were to $800
It's only my opinion, but $800 won't begin to pay for the modifications needed to put the Chevy in your car. I'm sure you could buy a small block MOPAR at a local junk yard and install it cheaper.
Just to give you a heads up. For the SBC you'll need to customize a way to hang the transmission as it will not bolt up to the MOPAR trans location. The engine mounts will not bolt up to the existing setup so that will need modification. You'll have to modify the electrical system. New transmission lines will have to be customized. Depending on the cooling system, you may need another radiator. There will be OTHER costs.
And based on many builds and custom cars I've worked on, you should start a list of all that is needed to modify (SBC engine and MOPAR mods) what you require in order to do your swap (you will miss a few things). Do not low ball anything, be realistic. Then when you think you have everything in order (customizing mods and paying a welder and fabricator to get it installed) to do your job. Then multiply what you've estimated by 2 times your estimate and preferably by 2.5 times your estimate.
To be truthful, in my opinion $800, will not even come close to the cost of doing this. If the /6 engine is in good shape, and I know you don't want to hear this, keep it until you have what it takes to transplant a MOPAR V8 into the car. It's well known fact that good horse power costs "cubic dollars". If you had a Chevy this would not be expensive at all and $800 would probably do it as long as all parts were in good shape. Rebuilding either the engine or trans mission would eat up most of the $800.