The 14 bolt SF 6 lug is extremely common on 1/2 ton suburbans. Look for the RPO JB6. I just finished this swap a bit ago...
Avoid the factory posi. I looked at 6 rear ends with the G80 posi, every one was bad. Several wrecking yard guys told me they'd never seen a good used G80.
The main weakness of the 14 bolt SF is the gear carrier. An Eaton Trutrac will fix that, but is spendy. Outstanding posi though, and cheaper in the long run because of no clutches to wear.
The SF has better ground clearance than the FF, the FF is stronger. The SF is MUCH stronger than the 10 bolt, and much heavier too.
You'll need the U bolt backing plates from the donor vehicle, the plates that go on top of the springs. Your current U bolts will work fine.
If you have a 4WD, you MUST get a rear end from a 4WD. The 2WD version is narrower. The 4WD is 67" wheel mating surface to wheel mating surface.
If you have an OBS, any OBS will work as a donor.
The brake lines and parking brake cables will hook right up.
You'll need a conversion U-joint. Your current drive shaft will work just fine.
Get the brake proportioning valve from the donor vehicle. It'll need to have the same ABS setup as yours for it to work. If the ABS is different, find a Brake proportioning valve from a JB6 vehicle with the same ABS as yours. And yes, the proportioning valve can be removed from the 95-99 ABS units. They look to be integral, but they bolt on. If you don't swap the P-valve, more properly called the combination valve, your brakes will be dangerously out of balance.
If you have the '95 - '99 4 wheel ABS, the P-valve is still available new. If you have a '92-'94, then used is your only option.
The 11" brakes on the 14 Bolt SF are a HUGE upgrade over the 10" drums on the 10 bolt. Not just size either. The 11" brakes are duo servo type, the 10" are leading-trailing type. IMHO, the best brake upgrade you can make if you have 10" rears. My brakes went from crappy to outstanding.
If this is really just for the weight, it's easier & cheaper to bolt 100 pounds of lead into the cargo area. Or go with a custom rear bumper. A good posi will make more difference than the weight.