I've got a mid 80's olds 307 that I was told came out of an 80's 442 I was wonder if id be able to use the heads of an older 350 olds on that 307

 

Heads from WHICH 350? The 1977-up motors used 1/2" head bolts and the heads will bolt directly on. The 1968-76 motors used 7/16" head bolts so the holes in the heads need to be opened up. Of course, you also need to verify the combustion chamber size. The 307s used heads with 64-67 cc chambers, same as the early 350 heads. The No. 8 heads have 80cc chambers that will drop CR so low that you can run kerosene and not detonate. What size valves are in those 350 heads? The 350 has a 4.057" bore. The 307 has a 3.800" bore. And finally, which year 307 exactly? The ones with 5A heads will have compatible intake and exhaust manifolds. The ones with 7A heads will not.

 

If you have 5A heads, don’t bother, not enough gain. The only heads I would mess with, and even this is a stretch, are #3 and#4 heads from a 330. Smaller combustion chambers but You lose .024” from the thicker replacement head gasket. Still need to drill the head bolt holes to 17/32.