Welcome, sounds like a deal???
AMC engines have the size cast right into the block, look under the motor mounts on the side.
You'll see an upside down 401 or 360.
Far as a different engine, anything will fit the hole.
Swapping transmissions, transfer cases, exhaust, motor mounts, driveshaft modifications, etc. etc. etc.
Usually makes swapping not worth it, unless money isn't an object.
An AMC 401 will bolt right in w/ no modifications.
You should have a Dana 30 front axle, and a Dana 44 rear axle.
Transfer case should be a Dana20.
Transmission should be a TH400 w/ an adapter plate.
Only 2 places make lift kits.
BJ's Offroad, and Hell Creek Suspension (eBay) http://motors.search.ebay.com/_W0QQsassZhellcreek
Many things can be done to make it more reliable.
Parts are mostly still available, what you're looking for, dictates where to go/look.
They can usually be found w/o too much trouble.
I have a '73, if you want some additional info just ask.
So far I have upgraded the wiring w/ a complete 1979 wagoneer harness.
Upgraded the axles w/ 1977 Dana 44's w/ disc brakes.
Engine was replaced with a strong '79 360 and DuraSpark ignition.