Cragar SS Lug Nuts for my '66 Barracuda

I can't answer that. I didn't know there were tapered washers available. Get the correct ones that Cragar recommends. Now, looking at the photo, if the mounting surface around the lug nut hole is the same dimension, I would think the flat washers are what you would want.
I stand corrected, the washers are not tapered, but "Offset oval/Center oval."