Phil, In my case the guages are 400F and I found the smaller diametre ring a little tougher to pry on so I cut it with a dremel cut off wheel. I ran out of patience trying to find the 3M products so made a small stainless bridge and soldered it in place to hold both ends of the ring, then some JB Weld to finish the job.
In your case though get a short piece of 2x6 and with a hole saw or whatever drill a hole just slightly larger than the bezel but smaller than the ring itself. Line the hole with felt or something soft and tip the newly painted guage upside done into the hole so that the ring rests on the outer edge of your hole. Then gingerly reclamp the ring. Don't use pliers to squeeze it though as you'll mark the top side of the ring.
Your guage looks a little rough, maybe you should test it before investing a lot of time.