Well, I would say the deciding factor would be the combustion chamber volume. The smaller the combustion chamber the more power can be obtained. The 327 cylinder heads would probably have larger intake runners for better flow. The 327 would probably have a larger combustion chamber also. So take this into consideration. If I may make a suggestion These should fit your engine application though I am not much on the large 67cc combustion chamber. They have 165cc intake runners and are fully assembled to boot. http://store.summitracing.com/partdetail.asp?autofilter=1part=SUM%2D152123N=700+400304+4294925079+115autoview=sku And they are a steal at under $300 each.
They are not listed as a 307 engine part. I am not a chevy man, but I figure if you can get 327 heads to work, these should too. You may want to do more research on chevy engines to make sure. If they are not compatible, you may want to swap out to an engine that is more common, and easier to find performance parts for.
