. . . a 89ish 4x4 Blazer to a 95 S-10 Ext Cab 2 wheel drive? Wonder if parts such as the engine, tranny, axles, etc. would swap over?

No to transmission, and axles.

Motors possible, but I would avoid it.

There isn't really anything that I would want to try switching over. They are just completely different rides when you compair 4wd to 2wd.

The rear diff on the 4x4 is wider
Ant the tail shaft on the transmission is different. The gearing might be as well