Like I said I'm going with the Tamiya gear box, again I have been planing and gathering parts for a while and when I started CR servos weren't available unless you converted them... and I didn't want to try that with these early builds. Now that you can buy them converted I would probably use them if I did another one.
Anyway I use this gear box at 114.5:1
And again I replaced the Tamiya motors with JK racing Hawk 7 motors, they will have no problem with 7.4v
I hacked the bottom out of the dozer so I could slip the gear box in... I filed off some of the gear box to get a smooth fit.
There is plenty of room under the drivers seat,
I angled it back just a little to miss some plastic the protrudes down, on the topside it's the space between then drivers seat and the side consoles. You could cut it out and just put some sheet plastic in there and gains another 1/4 to 1/2 an inch if you wanted.
No real issues so far pretty straight forward, I cleaned out most of the inside of the body cause I know I'll need all the room I can get, my wiring is still a hot mess... now I have to get to work on the drive gears and get them mounted.