Here is a Disneyland / Walt Disney World Galaxy's Edge Droid Depot C Unit body extender for attaching R Series Legs to a Chopper style droid.  Since the C Series droids have a shorter body than the R Series, the Droid Depot offers these extensions so that builders have more options to customize their droids.  It snaps easily on the bottom of the C body and you simply snap your middle wheel or leg into it, screw on your standard R legs and the droid will drive normally.