Having put a 305 then a 350 in an 82 malibu (to replace chevy v6), same basic car as yours.

Rad should work - we never had a problem, and ran AC too.

STRONGLY MOST DEFINITLEY recomend front V8 springs - we tore the y-pipe off more than once, and speed bumps would beat the car up BAD.

we used the motor mounts from our donor car - 78 camaro, so these should be pretty common/cheap to get.

to use a chevy engine you'll need a chevy trans, teh BOP (buick/olds/pontiac) engiens use a different bolt pattern If you want to keep your tans, you could try a 307 olds, 301 or 350 pontiac motor