I have a 305 tpi in my 91 z28 and I'm looking to chang it to a 350,what year 350's can I use and what heads can I use to keep the tpi and computer?what will I lose for power if I use 305 heads on a 350?

 

you will have to use heads made to work with the TPI if you want to retain that. As for the block, any gen1 block will work, but only the 87 up blocks will be able to use the factory style roller cam set up. You can use older heads for regular intake mani's but you will have to elongate the middle holes on the intake to line up with heads. Doable with a dremel but dont expect it to be pretty.
As far as I know, it is very unadvisable to use 305 heads on a 350 since the air the 305 heads are made to move is significantly less than a 350.

 

I hear about people putting 305 heads on 350's all the time... jacks their CR thru the roof

 

Depends upon what pistons are in the 350. The typical factory dished 350 pistons (or their aftermarket replacements) put the CR with 58cc 305 heads at about eye level.

9.7:1 in my case with 10cc dished/valve-relief Speedpro pistons. Turns out these "305" heads have 64cc chambers.