[dtw]

This would have been covered by a search. Those aren't case numbers, they are casting numbers for the left and right halves. All things being equal condition-wise, go with the second case. The 4R & 3R refer to the casting revision status - the higher the number, generally, the beefier/stronger the case, up to 7R (the last revision of the magnesium case). Yes, it was normal to have different levels of casting revisions between the left & right halves.