When I was looking into hub caps for my truck I ended up purchasing a few different used ones off of eBay. I wanted to put early 50's GMC hub caps on my 59 GMC.
They FIT!
As a bonus I now have some cool old GMC hubcaps on my shop wall.
Are you saying that your 60 GMC should have the same hubcaps as a 59 GMC to be correct? Or are the 60 hub caps rare and you are planning to settle for 59 hub caps?
Quite often there are a set of 59 reproduction GMC hub caps on eBay.