Not sure what you will be gaining. If you go to the track, you want the tank to me fairly empty so you are not carting around the extra weight, so the weight distribution will not help you much there.
The actual weight distribution on an RC is not that bad to start with. It's 55/45 as it comes from the factory. Not bad there. Not sure what it is on a QC.
Transferring a couple hundred pounds is not going to help your traction problems. The problem these trucks suffer from is a rear suspension that is just one generation above a covered wagon. This set up just does not allow for much weight transfer during hard acceleration. There are many vehicles out there that weigh less than these trucks, have as much power, or more, and do not have the traction issues we have.
If you really want to relocate the tank, use a fuel cell with break away lines. You are moving it to a location where it's more supceptable impact damage in the event of an accident. You do not want a fire.