I don't know about putting a .70 or a .90 in the gen but I do know that you can't just drop another .46 into it. You would have to do some major modification to get it to work. As it sits now the motor takes up 3/4 of the available space in the "engine bay" also the configuration is all wrong to add a second motor since the tranny sits off to one side of the "engine bay" I'm not saying it can't be done but I would think that you would have to be very good at fabricating parts to get it to work.
Hope that helps,
Buster