
Moderately strong, yes, but far from indestructible. The Turbobricks guys making 300+ bhp are forever complaining about the M4x series being too weak, but then the most common M46 (4spd+OD) is supposedly the weakest too. It's all about driving style...abuse the box (even with a B14) and eventually it'll break. 5k clutch-dumps....me?!

The 47 and 47R are definitely different boxes, and I don't think it can be down to the bellhousing, as this can be unbolted. I'm guessing it is related to mountings (and maybe the linkage?), since the 'R' boxes lie on their sides. The input and output shafts may well also be different.
cheers
James