There's a lot going on here... Lets look at one thing. Lower Wheel Speed.
The DRB-REW Rear Wheel Drive Evolution Weight Shift machine is capable of handling a large rear spool. Why? To lower the rear wheel speed.
On low grip surfaces, the rear RPM easily can exceed grip. You have a few options.
Use a torquey motor like a 21.5T.
Reduce your forward Speed
Reduce your EPA (crude method)
Change your spur and pinion.
Change your rear drive.
Of all the things I thought about for the REW, a large rear spool was an option I wanted to implement. So the rear shock tower was designed to accommodate this.
The key to this on a Yokomo belt drive system is 2 fold
The Yokomo drive kit for 1.3 Countersteer.
this is the DIB link. http://www.teamyokomo.com/partslist/ib/parts_ib_fcd13.html
The kit includes a 27T pulley (which is fine for CS) but we are looking at RWD here.
We will replace this with anywhere Alloy Pulleys from Sakura from 41T to 45T
The pulleys seat well in side but the screws are very slightly offset.
A very slight file to the inner section of 3 is enough.
Then it all bolts together. You should be able to run a lot more power through the drivetrain.
Belt size will need to be adjusted depending on the drive pulley and rear pulley options.
This is just one method so b careful of load on your motor and drawing too much power from your esc.
Always monitor temps for tuning.
For countersteer you can use the opposite on the front. Mounting to a One-Way requires six small screws and bolts. Simply clamp the oneway to the pulley.
Clearance in the front of a DIB and DRB will require some grinding. when you go more than 43T.
to the shock tower, Steering rack and steering mount.