a guy I know has a '66 chevy c10 that his dad or uncle bought new... I asked him about the wheels once... and this is what he emailed me(I saved the email) :
I checked on the wheels in my garage like I told you I would at the show...
They have just 3 dimples, not 4. They are the original wheels that came on the truck.
Just letting ya know.
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On my '65 c10 - I have 3 15 inch wheels that have 3 dimples and 2 15 inch wheels that have 4 dimples. I've been told the ones that have the 4 dimples are earlier/older late 50's/early 60's like 60-61 year model.
here is a picture of one of the '3 dimple' wheels on my truck:
http://matraca.home.mindspring.com/img09272003/03.html -W