It really depends on what he is trying to accomplish? putting an older engine into a newer car is actually illegal. Since his car is a 97, it is obd2. If they do obd2/emissions testing where he lives, then the car needs to remain obd2 or he will fail inspection.
So if he doesn't care about obd2/inspection/etc. then just keep it simple and go fully obd1. If he needs to keep obd2, then he needs an obd2 b18c1 ecu, and an obd1 to obd2 adapter (
www.boomslang.us ).