[MARKDTN]

Originally Posted by RustyPile

This is incorrect information. the 307 has a 3.875 (3 7/8") bore, while the 350 has a 4.000 (4") bore.. Basically, the 307 is a stroked 283 with the same stroke as 327.. A 350 is a stroked 327 using a 3.47 stroke crank. Meaning a late 327 and 350 are the same block. The short lived 302 had a 4" bore and the same stroke as a 283... The only thing in common with ALL these engines was the rod length -- 5.7".

That post is 10 years old, but perhaps what he meant was that all large journal small blocks (except some 400 with more freeze plugs) look similar and are dimensionally the same outside. 2bbl vs: 4bbl is a good clue but in the last 52+ years of these trucks a lot may have been swapped around. Oil dipstick location helps with later blocks as does 1-pc rear seal if you can see that if it's on the ground with no flywheel. Honestly the stamp pad is the best way to tell what it is without too much work-assuming it's never been built and decked.