This question comes up often and the standard best answer is to modify the original frame for what you want. The reasoning behind this answer is the fabrication of all the body mounts as well as getting it mounted to a newer frame so the stance is correct and looks right. Example"there is a 57 chevy around here that has some of the best fabrication and metal craftsmanship you will ever see mounting it to a 80's Cutlass frame.
unfortunately when it was all done it sits about 6" too high and doesn't look right, looks like it should be a 4 wheel drive"
It is much simpler to graft a late model front frame clip to your existing frame if it has not been damaged to be un-usable or use a suspension and motor mount kit from one of the aftermarket manufacturers. There are various opinions on what pieces to use and why each feels they are the right pieces for the job.
Being it's Dodge then I would be looking for a Chrysler sub-frame and a 340, 383 or something along those lines.........
just me and my weird thinking.