Does anyone make an adapter to put a 3 1/8" gauge into a 3 1/2" hole? Got a friend who's got a full set of gauges, but the speedo doesn't fit into his gauge housing (a Haneline engine turned ones, so you can't modify it!)
I ran into that same problem putting modern gages in a 38 chevy truck. I made rings out of stainless steel a little larger than the gages, then rounded the outer edges and buffed it. when trapped behind the gages it looked like part of the gages
If you have one of those chrome doo dad and fancy light shops for semi trucks anywhere close you might snoop there to see if they have something. Otherwise after spending some time snooping I'm thinking you are going to do similar to what tb33anda3rd said he did and make one out of what ever material you feel looks right. He might see if the manufacture for the gauges he has, sells a 3-1/2 inch speedometer with the same bezel design and find out if he can just buy the bezel (uh I need to replace a damaged one) and then make an adapter ring that centers the speedo he has in that ring. something like this Ebay item number: 352548055822