tranmission interchange

I have a 78 510 wagon with an automatic transmission that won't shift into 2nd gear. I'm interested in converting it to a manual transmission, preferably a 5 sp. Talking to wrecking yards, their interchange books say only 78-79 will interchange. I'm new to Datsuns having primarily delt with Ford stuff. I understand that I have a L20B motor, that has alot in common w/ the "L" series of motors. I think I've seen that the L20B has a six bolt flywheel instead of a 5 bolt found in L16 and L18. What issues will I have with finding a transmission to interchange? Are the bellhousings common throughout the L series? Are there bigger or smaller sized flywheels, are they externally balanced or is the engine internally balanced or maybe balanced at the harmonic balancer? I realize that I need to come up w/ a hydraulic clutch setup. Help me learn whats involved and what I need to acquire.

You know what would be the most satisfying? Get a regular SR20DE engine out of a 1991-94 Sentra SE-R, 1995-98 200SX SE-R, or a 1991-93 NX2000 and use the the transmission from that. The engine will cost you $600 max, and the tranny should be about $200. Also, grab the front drive axle from any of those cars and you'd have one haul-ass 510 with an economical 140hp engine.

Keep in mind I have an engine that runs fine, and I'm not interested in racing or an elaborate rwd to fwd conversion. I simply want to replace the automatic tranny I have with a manual.