Hi
If I knew what machine it was intended for, I might
start with a controller like the one in the machine. It
already has much of the needed hardware and then
a simple microcontroller. Not need for high speed.
Say I was making it for an XT. Just find a similar XT
controller. A few interface chips to control the digital
part and the controller to send and recieve the MFM.
A little bit of signal changing but not rocket science.
Dwight