I'm about the same age as Don and know him well. I'll see him this Sunday at the Pomona Swap meet. I never heard of the wheels referred to as R wheels by American Racing back in '65-66. None of the magnesium wheels had the logo on them for liability reasons. American was aware of the shortcomings of magnesium in a non racing environment. The D was for disc brakes . I don't know why there were three distinct spoke designs except for brake clearance reasons. As I said before , the wheel used on the Bullett ( in aluminum ) were mainly drilled for GM cars. I saw a pair ( GM) in magnesium last Sunday for sale in Long Beach.