3 different types
73-77_no vin cutout
78-80 _same as above but with vin cutout
81-91
they will all swap from one to the other. I am running a '77 in my '89. And my friend runs my old '89 in his '76
The metal frames are all the same untill you get to 89-91 1 tons, K5's and burbans. Then the area around the radio was changed to made room for the larger radio. But the pads still fit, the bezel is different.
If you want to run the old one in a new truck, then look for one with the vin cutout. I haven't been hasseled yet but since my K5 is registered as a '89 but cloned to a '75 I would have to pull my pad to prove the vin. And my geuss is I'd catch crap over it too.