Converting 834B's chain drive train to the belt is not so easy. I used be using TRF415's pulley at first but different now. TRF415 pulley fits 4mm width belt, but 4mm is too narrow for this project. Popular belt driven 4WD have narrow belt, but they are using belt drive as reduction too. 834B's front drive system is just using for fronts, not for reduction. The internal gear's ratio what rotate drive pully is after second reduction. So its big torque acts to front drive system. That's why wider pulleys and belt are needed, it's for anti-slip.
I'm using 6mm width pulleys and belt now. The pulley is helicopter's stuff but I think it's JDM(Japan Domestic Market) product. It has same number of teeth as TRF415's, 5mm inside bore, 6mm width. That's good for 834B. Parts# is QEP16-52-1, made by Quick.
http://www.9129.co.jp/
There is no belt that can be fit to 834B in RC products. You have to find it out from industrial products. I'm using MITSUBOSHI BELTING's "STPD S3M". length is 453mm but I guess 450mm is better. In case of MITSUBOSHI, 450mm is unavailable. But other manufacture (ex.PIRELLI) may be selling that size.
http://www.mitsuboshi.co.jp/english/index.html
And some chassis modifications are also needed. 834B's nylon parts are not stiff. So the belt's tension let chassis be warped. In case of my car, I glued graphite plate on the front bulkhead's wall (bearing hole side) and change upper deck from stock plastic to graphite thing. Front side of upper deck was designed to don't twist bulkhead, that part is wider than stock and fit into bulkhead's groove. Of course main chassis must be graphite or fiber glass.
As a result, belt drive is good for the race because its low inertial mass and also good for gain chassis weight. It's easier than chain drive to do side by side race. But chain drive is much better for maintenance and easy to keep condition. So I usually run only chain drive 834Bs except for race. I will be able to upload more pictures of my BD Dog later.