The M47 was found in '87 and later 240 and 740 models. It's a true 5 speed, so it has no overdrive unit on the back, which makes it shorter. If you get one from a 240, get the driveshaft as well. It uses a rubber bushing at the point of connection to the transmission, unlike the M46. The M47 is an aluminum case transmission, so it is considerably lighter than the M46 iron case, and still lighter than the M46 aluminum case because of the overdrive on the M46.
It bolts up to any b21/23/230, no modifications needed, and it has the same gear ratios as the M46 (5th gear is slightly different, but they're both in the .78-.80 to 1 range).