Difficult decision. I would go after the rebuild. As mentioned anything could happen even with a new off the lot coach. If you break the project into smaller manageable steps with reasonable timelines it really isn't as hard as it looks.
Day 1. Mark, photograph and document all plumbing, wiring, and other aspects of the engine compartment.
Day 2. Drain ALL fluids and document amount drained.
Day 3. Disconnect all cooling and fuel system lines and remove as necessary for clearance,,,,
Hardest part will probably be keeping the A/C system intact so you don't have to recharge it considering the age and expense of the older feon. And when the day comes that you turn the key and the new engine comes to like your head will explode with pride of doing something few would attempt.
Go for it. Document everything as it occurs and post up dates so we can follow.
