CEN told me the .46 backplate fit the sh28. It didn't. But the HPI backplate from Hobbytown fit (close enough) and, with the CEN gear, washers to clear the extruding disk under the one way nut, I got a pretty good roto-start. I sealed the 1/8" gap all around with a tube of gasket maker. I use my drill with the CEN roto bit. Note: the HPI roto bit slot is different, use both gears from the CEN part.

Bill