Have not heard of a R in a Bravo drive. Seeing it with Alpha is understandable because things change to run in reverse. If its stamped then might indicate its been repaired. There has a R version on Black hawk drives
Almost {not almost) any Bravo lower and upper can be swapped on one another. Even the Standard, X, XR, XZ can all swap with any lower. The almost is after 1993, but if I was going to use one I would look for after 2000
Have not seen a 2:21 and my guess is its really a 2:20 or the person that has it doesn't know. Changing to a 1:81 would require a porp change