I have a disc for Developer 5. I don't know whether your reg code would work for that, and can't recall what the differences were between 5 and 5.5.
Thank you. I can't recall, either, although I seem to remember that 5.5 was pretty major for a "point release".
However, good news! The client is going to just have us rebuild their runtime in v14, using their old one as a model.
Nevertheless, I'll continue to comb my files and "old tech" piles to try and find an installer. I have fmd5.5 on this computer, but this computer probably won't last forever. I don't run across this type of ancient history often, but it happens. :-)