94 Sentra Question + Problem

I was wondering if anyone knows what kind of engines can fit into a 94 Sentra SE,and where I could find them also mine has been over heating and the coolent is fine but the heat will go from hot to cool by itself and on a side note the fan only works on 4 no other setting ... any ideas

In order to do a good engine swap, you need the SE-R transmission, SE-R axle, SE-R maf, and SE-R ecu.