Check out www.isspro.com

I need to replace all the gauges in my truck; I'm planning to make a new gauge panel (probably out of wood) with all Isspro gauges...they're pretty good quality and don't look "Performance-tacky" like Autometer gauges do (in my opinion).

You could also get a two-gauge pod that will bolt to the dash cover...if you did it right, it could even be made to look like it belongs there. IMHO that may be easier than ripping out the ash tray and fabricating something to go in there, and besides, the ash tray makes a great garbage can, as well as the cigarette lighter being useful as a 12 volt outlet.

How much do you want for that Cummins?