[ray_mcavoy]

To make it look as original as possible, you'll want a radio from a 1967 - 1972 GM pickup, Suburban, 69-72 Blazer, or 70-72 Jimmy. I believe the GM G-series vans also used a very similar radio from 1971 up into the 1980's.

There are probably other GM radios that will fit too. The key measurements are the shaft center-to-center spacing of 6-1/4" and the center rectangular opening of 4-1/2" x 2-1/4". That rules out a lot of the later GM radios (like the ones used in 73-up trucks for example) because those have a narrower 5-3/4" shaft spacing.