I'm trying to find what motor ( ci ) I have GM # 3994257. It came out of a 66 nova. Don't if it is the original or not.

There should be a 4-digit stamped code on the milled flat where the distrib clamp bolts in, see if U can read that. That tells the engine & car specifically.

I think in the main index here there is a list of block & head casting numbers that might help too.