Most of the Honda GXH50's are sold with a 5/8" dia. X 1-1/4" long shaft that is tapped for a 1/4"28 thread. The side bolt pattern is 2-15/16" square. Are you aware that there are two different 4G belt drives? The one that is currently available from bicycle-engines.com will not bolt up to the Honda motor. Its made to fit the new version of the HS Clone motor. Are you aware of the differences in these two motors?
ocscully