I guess I need to know... why go through the trouble? making that change look good would be a real problem, and may require access to a machine shop to make a new face for the gauge that would fit in the factory hole. Or if you took the guts out of a mechanical gauge and attached it to the factory face, you would have to calibrate it (unless you found one with the same range and swing, and this would still involve some machining to make it work most likely).
I take it you have done a google search to see if there is anyone outside of here who has done it... You can try to call manufactures and see if they might have a combination gauge that will fit the factory hole (hell said gauge might have boost and pyro in it, solving most gauge mounting problems in these trucks!)
If after all this you still want to do it, drop me a message and I'll give you my phone number and we can toss ideas around (I'm not on often, as I am in school for 13 hours a day... ).