i have a 1980 4x4 pickup and i just got a 1988 4x4 for parts and i want to know if the 5 speed(i'm guessing w56?) will directly bolt to my 20r to replace my L43 4 speed.
also is there a difference in the brakes between the two models and how hard would it be to convert my rear drums to disc using the brakes from the 88?

 

i do not believe the w56 will bolt up, it is a few inches longer than the the L43

 

the L-series transmissions in 1st Gen trucks are about 21" long
A w-56 is approximately 25.25" long
you would need to move the crossmember back and lengthen front DS & shorten the rear DS.

the 88 rear brakes are bigger. a good upgrade would be to swap the rear axles, the 88 axle is 1.5" wider on each side so you would need to get 1.5" wheel spacers or do a widening kit (like sky's off road sells) upfront to match the rear track width
you could also swap in a dual diaprahgm (sp?) brake booster from a later model 4runner or turbo truck (86-87).

try searching a little bit about converting to rear disc brakes

 

Yes the tranny itself will bolt to the motor just fine, however, as OC mentioned, a new transmission crossmember would be needed or re locate your factory mounts. And driveshaft length will need to change. if you have a short bed truck you can just find a driveshaft from a 84-88 truck and change out the flanges(second gen has large bolt, square pattern) for your first gen ones(small, rectangular pattern) or you could just redrill your pinion and output flanges to fit the second gen pattern. Even if you have a longbed, you could use any 84/5 front driveshaft since it will be of the right length to run the later model trans.

 

I also have a 1980 4X4 20r with a 4 speed. Will any of the first generation 5 speed transmissions bolt up to my truck. I am in colorado and looking for one if it will bolt up.

 

a first gen 4x4 L50 or L52 is the same length (~21 1/4" long) as your 4 speed L43.
The only thing you might run into is having to work on the hole in the transmission tunnel

later model transmission are about 25" long