I guess the "black colored" front hubs are probably aluminum too, just painted black? Harley-Davidson Racing had a rear drum kinda like this too? However, I think the rear drum on Leo Payne's Bonneville Race bike is this front drum, adapted for a rear drive sprocket? Correct me if I'm wrong. (Look how teeny tiny that sprocket is ! )
"What do you run for a front sprocket?" Answer: " A 21 Tooth"
"What do you run for a rear sprocket?" Answer: A 21 Tooth"