Will a 1997 Ford Explorer XLT V8 engine work in a Ford Expedition?

I sure it will fit in the engine bay, but the Expedition uses different engines and management systems. Unless you have a large bank account and plenty of time to work out all the bugs, I wouldn't. You would need to transfer over the engine, wiring harness's, PCM, exhaust, transmisson and other driveline components. You'll have over $10K in a vehicle that is worth $1000. Find a 4.6L or 5.4 that your Expedition original came with, that is your best scenario right now.

A 302 in an Expedition is a bad idea. Not enough power and it will not be smog legal.