I am looking at buying a 1993 6.5 block. It has some cracked pistons, but is otherwise ok. My question is are all 6.5 blocks the same? Is there a difference in an F or S series block or blocks that come out of bigger units such as 4500 trucks?

No difference between S and F but lots of differences between casting numbers over the years.

Do a search for 599, 141, 929 and 506 Those are the casting numbers over the years. There is tons of threads with info on them.

Dave

Will do. thanks,tom