A few compatibility questions.

What combination do you want to run; carb or fuel injection?
Differences between trucks is exhaust manifolds and power steering pump location. Steering pump moves up or down, and a little tighter toward the engine depending on vehicle. Engine short blocks are otherwise interchanchable.
Factory Magnum distributor cannot be used with a regular ignition system and carb setup. Factory LA distributor can go in Magnum's place to fix that with no modifications on carb setups.
Bypass hose mismatch is a minor issue. The hose gets a little weird bend but works fine.
I never tried placing a Magnum timing cover over a long snout LA cam. Easy enough to buy a short snout Magnum style camshaft. If I have time tonight, I'll slide a long snout cam in and check that clearance.