Thanks. I had seen
http://www.6502.org/source/integers/32muldiv.htm before but the way the comment at the top of the snippet on codebase64.org was worded, it sounded like there was a 16-bit multiply with 32-bit product on this site somewhere it was copied from. Based on the similar label names, variable names, and code structure, I believe this codebase64 snippet is a modified version of the 32-bit multiply with 64-bit product by Greg. I have also ordered the Scanlon book to see what the original routine looks like.
A google search of "site:http://6502.org/source/ license" came up with zilch for me, and only one page of results for "site:http://6502.org/source/ copyright" so it is not always easy to tell if something in the source code repository is an orphaned work or public domain or what. Have you considered having adding a note at the top of that page about suggesting licenses when people email contributions? Github does a good job of suggesting people add licenses to their repository for example, so it's usually pretty easy for me to tell how I can use a repo.