By using direct proportions to convert 12g (using a .729 bore) to 8g bore/chokes, it works out to-
IC .010 = .012, M .020 = .023, IM .030 = .035 and F .040 = .046.
My bores are R .846 and L .847. R choke is .828 (.018) or LM. L choke is .831 (.016) which should also be LM.
I know someone will double check this and definitely tell me if I'm wrong.
Using the 3.14 x radius squared I still come up with LM-M choking.