I don't understand the question. You need a setup simular to how Brad's bike is, just don't need to have the jackshaft/axle as far away as he does. The gear on the end of the axle just needs to be a few inches away from the drive wheels. I'll try yo give an oversized visual, so imagine two of the same bike with from the seatpost forward cut off and where the crank goes still intact. Put the drive wheels in each one just like it would be if it was stilll a whole bike and place them parallel to each other say 24 inches apart (the distance doesn't matter, just using it as a referance), so both of the back halves are side by side with the seatpost facing towards the front of the bike. Next you have an axle with two single speed gears at either end of the axle and inline with the gear on each drive wheel going through where the crank would be at. put a multi speed cassette or single speed gea in the middle of the axle inline with a crank at the front of the bike, now the only other thing is to tie the two back halves together using framing, but make sure it doesn't interfear with any of the chains. If you put the freewheels on the drive wheels, the axle will have to be completely in front of the drive wheels, if you have the fixed gears on the drive wheels the axle can be put inbetween the srive wheels with clearance for the gears, but the drive wheel on the right would have to be fliped over so the gears of both drive wheels would be in the inside to be inline with the axle gears. There use to be a freewheel hub and gears that would run on the left side of the bike instead of the right side, but I don't know if they are still around or how hard they may be to find.