I also ran into the "I have no way to program a GAL and I can't get a cheap programmer" problem, so I made a version of the mod which uses a ROM instead. In that other thread, there's a link to my GitHub with the program that built the ROM and the KiCad project as well as a link to the Tindie page where I've got the 9 units I built for sale. I'm not going to restock it unless Chuckphd53 falls off the face of the earth or something, since the GAL version is more compact and doesn't use a (relatively expensive) vintage ROM. In hindsight, I should have posted here before I had the boards made and assembled them all and avoided doing the same thing as Chuckphd53
.