Hi Terry,
Very big odds you won't need the expensive spacers to mount the sheeve. The spacers are for the Whizzer 24" wheel with the 5" rear brake. The 5" rear brakes were used on the Whizzer 24" Pacemaker and the 24" Ambassador. The 20" Sportsman also used the 5" brake, however the belt sheeve was attached directly to the rim [not the spokes].
Several EZM dealers have made rear belt drive systems and worked very well [Miles, Helmutt, Ray, myself, and several others], and in fact the original "silent power" only required a simple pulley change to convert to rear belt drive.
Only downside to belt drive is the unlimited possibilites of belt length due to frame, motor location, and drive system choices.
Good luck on the project, and I can tell you it is worth the effort as 98% of my motorbike collection is total belt drive.
Have fun,