Here's a quick pic of how I did the belt roller. The roller's shaft is actually a XX4 CVD front axle, with the round part cut off. The axle is the perfect diameter for a drive bearing, of course, and the little lip holds it on. The two "hat" spacers are just rear axle spacers (That go between the bearings and the drive pin). I just drilled the hole in the chassis by eye and adjusted it (file in or out as needed) as needed. The large "hat" spacers cover up the slightly-oblong hole, and clamp the whole thing tight on the chassis with a regular wheel nut on the end. Probably the hardest thing about doing this is you have to shave down one of the flanges on the drive pulley - just take your time with this and it'll come out fine.
