We have engines and compilers for Z80, 6502 and 6809 machines so it's probably an idea to start with one of the 6502 models. Modding the compilers is probably the simplest job, that's written in C. The engines take a bit more converting, obviously the way sprites and display routines are handled differ tremendously between formats. Kees van Oss did the Z80->6502 conversion so he's the best person to ask. He's on the MPAGD forums and in the Facebook group. I'd be doing the Windows editors so you'd need to let me know what you want and how you want graphic data output for the compiler. The best place to chat about all of this might be Facebook