Shorty pack fits right across the chassis. So its weight would be centered. The motor is slightlyoffset so movin electrics around could get the balance without added ballast. The onlyreason this wouldnt work is the pullies sit insidethe chassis perimeter. Simply making new ones that have a longer core would push them outside and make room for the battery. Pullies weigh nothing.

You could still run longitudal or transverse np with the same pullies or back to stock.
The only thing that would concern me is roars requirement for a normal 2s to fit.