Here is a step by step of my progress so far. Sorry that I didn't document the disassemble process of the gauge pod.
1.Here is the whole altimeter disassembled with the voltmeter.
2. This is the voltmeter dissembled and they are both the same diameter. 72mm.
3. Used a cutting bit on my dremel to cut out the face of the altimeter.
4.Used a cut off wheel to cut off the bottom of the voltmeter housing.
5.Used a grinding wheel to grind indent so the voltmeter would fit between the screw posts.
6.Before I super glued the two pieces together I had to grind down the inside of the altimeter
housing to make room for the voltmeter.
7.Used a piece of 0.080" lexan (the same thickness of the plastic from the altimeter gauge.
8. Super glued the lexan in place and when the glue dried I glued the gauge ring in place.
9. When the glue dried on the gauge assembly I painted the inside on the housing.
10. Had to trim a little from the inside of the gauge pod.
11. Here is the gauge full assembled.
12. Here is what it looks like all together. Its not wired up but I think It looks great.
Good Ship 
Most other states
