16.5" tires kinda hard to find - but here is one that looks pretty good:
http://www.tirerack.com/tires/tires....5THT&tab=Sizes
It is the larger of the stock size options for tires on the C20 (in later years, like 71/2 - not 100% positive about 67s). Here's a few pics of them on a 71 to give you an idea: