While browsing the modern hardware for the C64, I found a useful little project that could help speed up development significantly. Its a flash cartridge that uses a dual port RAM chip. The C64 sees it as a ROM chip, and a microcontroller feeds that RAM chip data. A PC feeds the micro, and you can make updates without restarting and such. A very handy feature indeed. I assume I'll have to make one myself, as the project seems to have gone dorment. Still very glad people publish stuff like this.
I've never made a custom board before, so that should be interesting. I kinda worry it would fry my C64 though, so there's that. I need to learn more about so many things for this project. It's going to be very difficult for me, but it will force me to learn tons of new skills.