engine years. options

[Marty68]

Hi, my name is Marty. i have a stalled out project in my garage. i bought a southern 68 short step.I was told it had a runnable 350 th350. got it home no compression ... and it was a 305. pulled them out and discovered the snout on torque converter BROKEN in half... not likely done by the 305. i disasembled truck welded in rockers and corners. i bought and never installed a used 350 that had low end knock local engine builder here replaced bearings and put in new used crank. said "it has a cam in it". i bought "used may be good th350" after buying a different house getting a better garage and changing wifes. (new one is awesome old one was nuts). i am contemplating selling 350/350 that i never installed and tackling an injected swap. my rear gears are 3.08.
question is... if i source an engine from car-part.com what year(s) 4.8 or 5.3. or 6.0 should i look at. is there a reason why not go with newer say 2010-2013 low mileage stuff? seems i have been searching reading for ever. i just want ease or assembly. drivability and mpg. i believe i can handle reworking harness welding bung on original tank. etc.