Each generation's cabs should interchangeable with their same type, might need a little adjustment, as with the beds. Swapping x-cabd and Std cabs will require moving the rear cab mounts.
Beds are also interchangeable, not just within the same generation, but at least across the first 3, they aren't a perfect fit, but they are interchangeable.
'79 2wd bed on '86, though could only get it to 1.5" cab-to-bed space.
'91 4x4 bed on '85 2wd long bed frame, had to move the front bed mount, had to use the 2wd springs to center the tire, w/the 4x4 x-cab springs the tire isn't off.
Seats between 2nd and 3rd gens are interchangeable as well, '91X-cab 60/40 seats in an '86. The seats are wider and just barely touch the doors, but the outer mounts lined up perfectly.
A buddy had an '87 4-Runner w/'94 4-Runner front and rear seats.
