Years ago I think Jim Dove (if I'm not mistaken) wrote an article on building the FE engines. In it he stated that the pre-64 FE blocks were a bit beefier than the later blocks. I mentioned it once and the guru's on FE Fanatics shot me down. So, I don't know if they were or weren't. The only thing I know was I read it from a reputable source I thought at the time.
SAME HERE JUST DIFFERENT it was not Dove,someone different.when i was a teen and early 20s, i was living,eating,breathing,sleeping,dreaming,FE engines back in the early 80s.i read an article that said 66-c6me blocks were the best bar none,the c6me-a weren't bad is how i remember it quoted.and the same article had a pic of dozens of FE blocks lined up in rows on the floor. and also i got shot down like an outlaw in the old west.