Here's what you need - Dash Inserts from Dolphin.

Go HERE and click on 54 Chevy Truck 5" Quad. Those will take up the half-inch and still leave a bit of room. They also are the only way to mount the gauges in your dash.

I covered mine with leather so they fit even better:
See Here

~~ Alan Horvath
1954 Chevy Pickup
Singing his praises in the
Passing Lane