Bushing mod for TheRuttmeister's Type-A Z-Rider

This is an alternate part for http://www.thingiverse.com/thing:5586, TheRuttmeister's z-rider design.

The original design calls for ten small bearings to ride the burnished guide rods. Based on Prusa's work with PLA bushings, I got to wondering if the bearings were truly necessary. After messing with several sizes of bushing on my Cupcake's M8 rods, I'm pretty confident that this can be made to work without the bearings.

I didn't include the M3 bolt hole from the original. Cleaning the