The platform is still FWD biased on SHO Flex Explorer MKS MKT etc using the 3.5EB AWD setup. However, FoMoCoSHO did note that in his 2015 SHO, the AWD gauge showed power TEMPORARILY going to 100% to the rear on a HARD launch. No one else has followed up on this, so make of it what you will.
I think you should try to find a much newer powertrain tho, have to swap around some minor parts from 2010-12 engines like the crank tone wheel, coils, some sensors, etc. But I think hi mileage EB powertrains with no maintenance history are a bigtime gamble. Don't want to cheap cheap, if you know what I mean.