To answer your question; the 14bolt semi-float out of Escalades, LD2500s, and heavy half K1500s should all bolt right in to a 1500. I believe the spring perches are the same spot as a 10bolt. As for the LSDs, I don't believe GM put any LSDs in these things from factory - they should all be Eaton G80s, aka the grenade80.
For reference, my last 3 K1500s had a 14bolt SF under them, and I've had to swap all 3. The first one was in my 96 K1500, which was a heavy half but only had a 10bolt, so I swapped it to a 14bolt. Second was my 97 K1500 6.5TD. I blew the rear end doing burnouts and replaced it with a 14bolt out of an escalade. And the last one was just changed 2 weeks ago on my current 97 K1500. There was too much internal wear and backlash was getting bad, so I completely refurbished another 14bolt and put it in.