There's a couple of guys in your country over at the Panzerkettan forum who are running the Jamara 480 HS BB motors with the 3-1 gearboxes. One with El Mod and the other with the stock electronics. He even posted videos of it climbing a hill. With a cooling fan and or heatsink this should provide plenty of torque. The motors are long can 400s. Meaning they bolt right up but are longer so you may have to bend the tabs so they don't hit the other gearbox.

Why don't you contact them for further information? Like you, I cannot go buying 4 set of test motors this time around, only one set and even that is not in the budget!