Thanks, Jeff.
I've heard the 80s were used for non-hipo ford small blocks, the 90s were used for the k-code and maybe the 100s were later for 351 or big blocks. Are there any reasonable rules of thumb like that? Or are they more or less interchangeable for our purposes? When I run across these items for sale, I'd like to make sure I know which ones are likely correct for which application.