Are you sure the drop center rims are intended for a bias ply tire? They may well be for a radial 20" tire.
The Coker website has little information on the drop center, but I would guess they are for a radial tire.
Tad
Yes, They are made for bias ply tires, I posted up those two pictures this morning did you take a look at those? The rims are intended for a 6x20 tire. When I ordered the blanks, they still recomend running a tube due to the high side wall.. no flap though..
I dont think you would ever find a radial tire that would fit a rim that narrow