I laid out the shape on the new gauge panel in AutoCad and cut it out in 1/8" ABS plastic.
With ABS pipe glue and epoxy I put the new panel into the front of the original housing.
I did the same with the center console gauge cluster. I removed the gauges.
Then I cut all the original gauge faces out of the panel leaving about a quarter inch border to bond the new panel to.
Here's the center cluster template done up in AutoCad:
I have the new gauge clusters temporarily connected to verify the wiring connections.