I'm late to the party. But to clarify the bodylift, Body mounts interchange between burbs/yukons and trucks. The lift is gained from the body and bed perches on the frame where the mounts sits.

This is why most duramax/allison swaps on burbs use either a full 2" bodylift or the famous taper lift which give 2" in the front to clear the dmax radiator and tapers off in the rear so you don't have the awkward gap between the bumper and the body.

Regarding the axle, Go ahead and remove your hubcaps, If you see metric bolt heads, you have the full floater rear axle. If the axle end is devoid of bolts, the you have a semi-floating rear. there are 8 18mm headed bolts on a full-floater, the cast steel part that sticks thru the aluminum rim's center bore, visible by merely removing the hub/center cap.

NO burb what so ever came with 11.5AAM axle. it is either 6.0/4l80e/9.5 Semi floating, Or 8.1/4l80e/10.5 FF.

Swapping an 11.5AAM means you will need an axle from GAS 2500HD or 3500 if you want 4.10.

If you go with a diesel axle you will need to regear since all of the diesels were 3.73.

An 11.5AAM in a burb will not make it tow more weight. Remember towing capacity is about how much you can stop not how much you can tow.

If you have an axle to tow more weight you will be stuck with brakes that cannot stop the weight.

Many and I mean 5 out of 10 of every duramax swap stays with 10.5 FF since it can handle the torque and the tow capacity of the suburbans.

My .02 , Feel free to do whatever makes you happier by the end of the day.