Two problems I'm trying to solve
 

I have a 1993 Mazda b2600i. Took it to a mechanic who says it's the distributor. Says a new one is like $650. Told him I'll try to find one elsewhere, but I'm having trouble figuring out exactly which one I need online. I'm finding most parts sites at not detailed enough to know if I'm getting the right part. Can anyone help?

Second, I'm having trouble with the 4x4. I was stuck in the snow one day, got it out, but in the process the truck made a loud "Bang!" On the way home I noticed it was revving high. Realized I had it in four wheel. When I tried to put it in 2High, it wouldn't drive. So I have to leave it in four wheel. Weirdest part is, I'm pretty sure it's only driving with 2 wheels, even though it's still in 4High. Any ideas?

What symptom does the mechanic say is the distributor? Advance auto parts has a reman for $190.00. As far as the 4x4 transfer case shift problem it likely got in a bind. If you are lucky you can pull the fuse or disconnect the battery to clear any codes. Sometimes they will reset and work fine. The bang could be problematic however.