I got to use CP/M briefly on a DEC Rainbow machine in the 80's. It was very similar to DOS but IIRC there were quite a few differences at the detail level. I remember seeing some ads for Kaypro's but I don't think I ever saw one in real life... What sort of issues are you having with the serial port? You might need to jumper the flow control pins if you can't disable flow control. I'm sure the pinout is documented? I had to deal with lots of oddball serial ports way back when, I might even have some breakout/jumper RS232 adapters lying around.