ORIGINAL: MinnFlyer
Aw hell, that's easy.
File out some holes in the front plate so you can get a screwdriver in there (Fig. 1)
Then make a plywood plate like in Fig. 2
Loosen the mount screws just enough so that you can slide the spacer down between the mount and the firewall. Re-tighten the mount and, Voila!
I'll be right over MinnFlyer.
Ken
Not sure what you meant by sanding down- The plywood spinner ring. It is only 1/8" thick.