mad force conversion to twin force

[tonka truck]

no 3 spd, I want to take the gears out and replace with the motor mount and spur gear from the twin force.

I was looking to run two seven cells packs (GP3300). What speed and runtime could I get.

Also, can I just drill into the MF chassis plate because they look kinda the same in the manuals.

I am really not sure why the gears stripped. It seems that my setpu from the shop was off. Anyway just want to make use of the truck rather than it gather dust.