Is the sole purpose of this machine going to be winning at the lights?
If so then perhaps you can afford to think a little outside the box...
1. Fit a car auto box, 2wd.
2. Uprate the back axle and fit some grippy rubber
3. Reduce weight. You've already lost the TX box. Smaller "fuel cell" type tank, rag-top, strip the back out completely (no seats/carpets/sound proofing). Lighter wheels (alloys).
4. Small wheels to keep the gearing down
Of course you're still going to need to uprate the brakes but if you're 2WD then it makes the front axle a little easier to do.
This will make it fairly quick but very neutered for anything other than dragging off the lights.