will a 383 squeeze in a 73 duster?

tell me more about the sub frame connectors, first time this has been brought up

Any engine with a sizeable amount of torque will try twisting off the front subframe from the rear. Worse case is cracks and doors won't align after a while. The connectors tie the rear and front together. Do a search, you'll probably only need the ones that are welded at both ends not the ones that also come up through the floor and are welded to the body.