The older, newer engines will be a easyer swap like Crenwelge suggested. A 235 or 302 might almost bolt in with a few minor changes.

The newer 230-250-292 will be more work due to motor mounts and crossmembers. With the 230-292's you can get parts at any local store, use about any transmission, and any late model rear axle. You need to decide what type of driving you want so you can gear it right, 3.08 to 4.11????

I like my 250 with T350 auto and 3.08 rear axle. It runs down the road at 70 mph and gets 16 to 18 mpg. Parts are easy to find and the swap was,t to bad. Joe