Lots of differences in small block Chevy heads. Especially between 305 and 350 heads. Some were open chamber, some were closed. Some may have had 2.02 valves, others 1.94.
A friend of mine put a pair of 305 heads on a 350 once, and I didn't know it until I couldn't help him get it to run correctly.
It would grunt while trying to start and clatter going down the road if you timed it according to specs. If you timed it so it would start, it wouldn't pull itself hardly.
Didn't help that he installed mismatched heads too.
