[JesseK]

A potential design is to use dead axles with 1/8" angle aluminum as axle mounts beneath the 80/20. You'd eliminate the low quality bearing blocks while also moving to more efficient bearings on the wheels.

We used this setup in 2011, and were able to easily drop the center wheel using a shim. We also had to account for welding imperfections, and do so by treating each wheel/mount assembly as an adjustable block. Each wheel had precise spacers between the wheel bearings and the angle aluminum mounts, which meant that once we mounted the two angle pieces, the wheel would never shift side to side (thus throwing off the chain). The angle block didn't perfectly line up with the frame members, but the sprockets did perfectly line up with each other. You can account for your own imperfections with 80/20 by drilling the hole in the angle aluminum relative to the 80/20 channel, rather than attempting to drill through the 80/20.

Once the sprocket alignment is set, you really just need a way to make sure the bolts don't slip in the 80/20 channel. This can be achieved with an imperfect hole through the 80/20 at the right spot -- a hole that doesn't need to go through your wheel mounts.