The gauge assembly and speedometer are held in by studs welded to the back of the dash and 3/8 (IIRC) hex nuts accessed from the back. Use a nut driver and the braille method to get on the nuts. There are 4 per assembly. Once you have the nuts out, the assemblies go out thru the back. Here's a couple pics of the gauge assembly showing the ears where the studs go thru. This is off a Chevy, but your GMC will be the same.
Kevin 1951 Chevy 3100 work truck Follow this saga in Project Journal Photos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together.
