The dash was a custom unit in 78. It contained the Tach, and speedo, set like a P30 C10 truck, but in a custom fabricated ABS sheet. Then there are the separate gas, vacuum, temp, volts, oil pressure and the non working clock. All of those are individual gauges as well.
On my 78 the ABS sheet that was the base for the gauge package was covered by a sheet of aluminum that has a wood Grain finish. This was bent to fit the shape of the dash and held on with screws into the ABS. I do not know if this was just a dress up plate or a way to strengthen the dash itself.
In my opinion I would use the face piece from the original dash, sandwich it with sheets of aluminum bent to the same shape and then drill the openings as needed for the gauge layout. Since it comes off in one piece you should be able to mount the gauges, terminate the wiring into some multi position connectors.
This then allows for ease of install as well as removal. Once you have the holes drilled you could burnish it to offer a nice finish, or get a carbon fiber skin and add it to the aluminum surface.
WBCCI #5501 AIR # 49
1978 Argosy 28 foot Motorhome
Wise men talk because they have something to say; fools, because they have to say something. -- Plato