You'd just use the ECU and engine harness from the donor car, the older Mazdas are ridiculously simple in the electrical department. A splice-in would be relatively easy (though it takes a pretty long time on an OBDII vehicle). Aftermarket engine management wouldn't be much more work at that point either, though it would be pretty pointless unless the donor engine was to be boosted or heavily modified.

Or in the case of the RF, toss the ECU in the trash and feed it like 3 wires.