The font was different as well. IIRC, it changed again in 81 or 83.
Be careful with that, most of those are for a diesel engine and will not work on a gas engine. The use different inputs.
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For the most part the C60 parts are the same as the light duty trucks... as far as body, interior, and cosmetics. Obvious parts in these areas will be specific to medium duty, i.e. vacuum gauge, fuel/tach combo, etc.
I would think the most important information to look at is where it was manufactured. Then which company.
Sometimes the most expensive isn't the best too.
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The price depends on where you buy them from. 15x8 is factory for the truck IIRC. Trim rings come in 2 sizes; 2" and 3" or deep dish, the 3" ones are for the 15x10s IIRC.
You can find the rims on craigslist/facebook, prices vary on seller, your area and if tires are on...
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https://www.chevyhardcore.com/tech-stories/drivetrain/12-bolt-rearend-guide/
https://www.hemmings.com/stories/article/gm-12-bolt-axles
https://itstillruns.com/chevy-12-bolt-identification-5601809.html
Hold your britches. Don't get yourself in a ruffle on something you have no control over. People are buying C/Ks cheap and flipping them, why, because they can. You may not like it but it is just how it is. People want older vehicles and they are going to buy them if they can. Think about...
Welcome to the site. Seeing how it had provisions for a headliner it may be a Cheyenne pkg but the dealer could have installed that too.
Does it still have the SPID in the glovebox?