Duramax core support/radiator is 2" taller than the gas counterparts, hence the need for the body lift pucks. Being you're using a 2500 Sub, though....it might all fit without the lift. You'll just have to deal with it when the time comes. This thread has the puck heights:
https://www.dieselplace.com/threads/where-to-buy-progressive-lift-pucks-for-suburban.770609/
Found this write up. It may help you:
https://www.dieselplace.com/threads/yukon-duramax.148819/page-6#post-2134993
The 2500 Sub is like the 1500hd/2500 pickup as far as frame and body height. You either need a 2" body lift or the staggered lift blocks to fit the Duramax core support into a 2500 Suburban.
You will use the Duramax engine/trans harness but use the Suburban body and other harnesses. You have to run a wire to the cluster for the wait to start light to work. You also have to rewire the ECM relay so that the ECM controls it instead of it being switched on by the ignition switch like gassers do so you don't get the P0612 code.
Getting your fuel gauge to work with the factory dual tanks and the fuel transfer pump is 1 of the biggest jobs to do. You have to take the gas fuel pump out of the front tank and put in a Duramax pickup assembly. The rear tank unit can be kept, but I highly recommend putting a check valve in the line going from the rear tank pump to the front tank so fuel cannot transfer via gravity. The Duramax ECM freaks out if the levels don't move how it thinks they should, and defaults the gauge to empty. It is also recommended to modify your fuel filler so that each tank has a hose going up to the filler to prevent fuel from sloshing from 1 tank to the other.
You have to modify the wiring so the ECM powers the rear transfer pump instead of the front tanks fuel pump. The pump relay in your fuse panel ran the front tanks pump and there is an auxiliary relay mounted outside your fuse panel that runs the rear transfer pump. When you hook the Dmax harness into your Suburban harness, it's fuel pump trigger wire will command the pump relay in the fuse panel that originally powered the front tanks pump. And the final step is to get a cab & chassis dual tank OS in the ECM, correct the tank sizes, and setup the level unit values.
I'm sure I'm overlooking alot of stuff, but this is a basic rundown. If you're on fakebook there is a duramax swap group with alot of info in it.