Just so you know, the Jagdtiger, while built on what was basically a King Tiger chassis, was actually slightly longer than a King Tiger. I think they stretched the KT chassis a lot like you would stretch a car to make a limo.

As for motors, you might want to look at the motors I put in my Hetzer. They're made for electric bikes and scooters, and have plenty of power and torque. I actually had to set end points to slow it down a bit as it was way faster than scale speed.