How do you know it's overheating, purely by the gauge?
as with the fiesta/puma conversion, depending on which ECU you use, you may need to swap some wiring over on the ECU as the temp gauge will read backwards.

As for the AC compressor, it has absolutely no bearing at all on the water pump.this won't be your proplem. It's easily removed, it's only held on with 4 bolts but you will need a new shorter aux belt.