I haven't seen enough 68 center caps to tell you anything more but any factory original caps that I have seen do have those double ridged flutes. The 68 centers also have a soft rounded outer edge around the edges of the hat, and not the pronounced sharp edge as seen on the edges of the 69 hats.
Maybe post some clear pictures of the ones from your 68 car both inside and out with close up shots from the hats and the return edges?
__________________
I like solid lifter cars, big cams and cars w/ 3 pedals in them. 
|