If you could take the drive train of the Gen II Volt and the battery capacity of a P100D and put them together what kind of electric range would you end up with factoring in the extra weight, the efficiency of the volt drive train, etc?
What kind of car are you putting it in? Range is affected at least as much by the load side (weight/rolling resistance, aerodynamics) as it is by the powertrain itself.
The Suburban version a few folks are proposing based on the size/weight of what you asked for wouldn't get nearly as far as either of the source cars, because it's a huge heavy car with fairly poor aerodynamics (hard to make bricks slippery, I'm sure GM is doing the best they can with it.)
It's also not the way I'd design an extended range car with ~90 kWh of usable energy - I'd use a much lighter, more compact generator in series that's only intended to match the steady state load, and on the rare occasions where it gets used, I'd hold on to a bigger buffer (4 kWh?) to handle acceleration and hill climbing. Sorta like the i3 REx approach in principle, but without the limitations that make the i3 so frustrating.
Since we're doing this by kitbashing at the moment, that'd also let me hang on to the Tesla drive motors and all that glorious torque and acceleration. (depending on the size/weight of the final car, of course.)