Perhaps this will head you in the right direction (assuming this is the part you need). No idea if this is the same as a 66 C10 but if you have an old one to compare it might be worth a $4.00 gamble. Also if you can bring the photo and description to a local parts store they might have an old timer that can find it:
http://shop.corvettecentral.com/1953...viewsTabAnchor