O.k. another question.  I have a L20 out of a '78 king cab, and a L16 out of a '73.  The L20 has an automatic tranny, but I want to put the manual tranny from the other truck onto it. Will it bolt up? If not, what will it take to make it bolt up? any and all help is appreciated

I believe the L-16 manual trans will bolt up to the L-20 engine.  The transmission to frame mount may need some changes. 

Do you know if I will have to change the flywheel over from the L16 as well, and will it bolt up to the L20 crank end? Thanx in advance 

I am not really sure, I have not actually done this.  I think the L-20 engine has a 215 mm clutchdisk diameter flywheel, and six bolts on the flywheel to crankshaft, and the L-16 has a 200 mm clutch disk flywheel, with five bolts.  I would go with the flywheel that came with the engine, L-20 engine, L-20 flywheel together.  I believe the L-20 engine, and flywheel will bolt up to the L-16 transmission.  The outer diameter  of the flywheel is the same.  My 1970 Datsun PU had a L-18 mated to a 5 speed that was orginally a 240Z transmission. If for some reason you end up using the L-16 200mm clutch disk, try to get a pressure plate for a Datsun 2000 roadster, they have a lot stronger spring.  Whatever works, let us know.

Thanx for the info, I recently pulled the motor from the 72 620, and it's a L20! Somenoe had swapped the motor out already. Now I have two L20's,....BONUS!!!:D