Found a little more info. Came on 2004-2006 Silverado's, so this was pre 2ML70 era. It used the standard LM7 5.3 engine and a 4L60E. The only difference was the flexplate and bellhousing. The flexplate was the rotor assembly and also used the motor for starting the engine, so no ring gear or traditional starter motor. The torque converter fit inside the rotor assembly. The bellhousing was the stator windings. The transmission was just a run-of-the-mill 4L60e. It was only a 42 volt system, so likely won't produce significant power levels.
I can't really seem to find stuff on ebay for these anymore. Almost a decade ago when I was fitting a 4L80E to the 2JZ this stuff was all over the place. Either way, for cheap and dirty this arrangement could be fitted to a redblock with off the shelf GM adapter components, controlled with an off the shelf microsquirt 4l60e controller and the motor controls are up to the user.