All the caps appear the same from the front. The difference is how they are mounted, and that is where people get confused. Half ton models had two versions, one of which utilizes a ring on the back that snaps into clips which are riveted to the wheel, the other has no ring and pops on over nubs formed in the wheel itself. ALL 3/4 ton and above trucks used the clip type mounting ring, but the ring is not the same size as the half ton. So, there are basically three styles of caps to be aware of, and only one kind will fit your C30. Sadly, no ring style caps are being reproduced.
Check out this awesome thread on identifying every cap you could imagine for 60-66.
http://67-72chevytrucks.com/vboard/s...d.php?t=702839