73+ i believe.
as far as drum brake hubs, you can usually find them cheap at swap meets. or you can do what you said and cut down a used rotor and make your own hub
Far I as remember, all A-Body drum brakes are SBP. And B-Body drum brake hubs won't fit the later drum brake spindle, the inner wheel bearing is too small. Maybe they fit the early drum spindle? Never looked at those.
B/E Body cars probably aren't an issue, but I suspect there isn't anything for the A-Body cars unless the B-Body hub fits the early A-Body spindle. Either way, the '73+ cars are left out.