This is hardly an FAQ. I've seen the question once in all the time I've been on RE5 forums. But what the heck, where else am I going to put it:
Be patient, look carefully, I made these notes for myself 20 years ago.
Sizes of all relevant washers are given lower left in millimetres.
More information than you'd ever want.
And the rack goes between the shock and the frame with a washer either side. You can see the parts book illustrates the basic "lift" grab rail. I've noted its thickness and listed the thickness of the typically available racks if you feel you need to compensate by changing washers.
Sydney, Australia. The new leaner, trimmer shed: RE5M, RE5A, GSX1100EX, GL1800/Champion sidecar