ls7 is too can based
The engine is just a lump of metal.

Engine management is another matter, of course, but you can fit different management systems to that lump of metal if need be.
If it were me, I would fit an ABS system from a 4 pot so it's not expecting to talk to the engine ECU at all and lose the TC. The Omega TC is only designed to stop stupid people crashing, IMHO. It adds nothing to the driving experience so why seriously limit your plans just to keep it working?
Ditto drive by wire. If the engine+management of choice happens to have it then fine. If not, put a throttle cable in. DBW adds nothing to the driving experience, it just removes the throttle cable.
ESP... Very rarely fitted to an Omega and, again, needs integration between engine and ABS ECUs and the addition of a yaw sensor, which I've never found fitted to an Omega.
The problem with all of these systems is that they have been configured during development for the combination of chassis, engine, transmission and braking system on the vehicle. The tools to do that are probably only available to Bosch and their partners in the development labs of major car manufacturers. Even if you manage the unenviable task of getting them to talk to each other in a modified vehicle, who's to say they'll work acceptably given that the vehicle has undergone fairly major changes?
Keep it simple, I say. Bin the gadgets and give yourself an easy life.
Kevin