The 5.3 truck is the most practical. Truck intake makes good torque and the pan fits. You loose ac generally. But there are ways to relocate it.
I am putting together a 87 k10 with a 02 5.3, sm465 to a divorced 3 speed brownie/np205 setup which will eventually be pushing front 14/60 and rear 14 ff 4.56 on 35" tires.
Cost wise I am $500 into the engine, around $1000 in fuel pump,seals/sensors/mounts, another $600 into relocating the coils, running forward facing turbo headers(na for now).
Still need to make a custom adapter for the brownie to np205, clutch, piliot, flywheel, steel bell, 6" shaft, rear driveshaft, middle front shaft for the belly, then front shaft. So another $2500 or so before even pulling the 10 bolts out for the 14 bolts.
Start building now and minimize the amount of time the truck will be sitting. Even properly planned out it is far from a drop in deal. 3k is about what a proper junkyard ls engine swap will cost all said and done.