I'd say an 11 litre rear engine leaves plenty of room and weight capacity for battery packs, then turn to the roof for any additional packs, maybe just to run the A/C and lighting if need be. You may be right and you may be wrong regards roof strength. Do the motors even need to be that powerful anyway? Gearing them down with a top speed of 80km/h may allow for smaller less power consuming traction motors.
Cars have been getting electrified by owners in the garages for decades. It's hardly that technically challenging to convert a bus when they're doing it to heavy haulage trucks.
Sounds like people want to bury the idea.