It really wouldn't be hard to modify an aftermarket 5 gauge bezel to accept 2 5/8" gauges(could probably do it with the stock one for that matter). Its funny, this 6-gauge Scott Drake bezel I am using I don't like because its based on the GT cluster...the GT cluster is pretty terrible IMO compared to the base model cluster...not because of the gauge design, but because the cluster housing is a hideous slab that sticks out an inch from the dash unlike the base model cluster that follows the curve of the dash and is much more aesthetically pleasing. I need a 6 gauge cluster...but I am actually only using this one temporarily, I figure I will have to make my own cluster that is based off the base model curves before I am happy. I actually cut the trim off my original 6 cylinder cluster to use as the basis for my future cluster project...besides, the cluster is a sore point with me because its virtually the only plastic piece I have left in my interior(well, that and my shift knob...but I plan on making a custom knob from granite)...I can't stand plastic in a classic car beyond vinyl(which is actually plastic covered cloth, but acceptable because it doesnt look or feel like plastic.)
P.S. There is another possibility...I have a standalone ECU and one of the things it can do is use bluetooth to connect to tablet or phone, so I am able to use the HUD mode to project engine parameters onto the windshield like this:
It is quite possible that someone out there sells some type of HUD compatible gauge or display that would work for you. All you would need to do is modify the speaker grill to insert a HUD gauge or device and install some HUD film on the windshield.