I'm pretty sure the rear part is different too.
I have a spare complete prop for an M46, and the rear section is made of two different diameters with what I presume is a sort of rubber vibration damper built in half way along.
The rear universal joint, on the axle, is chunkier than the one at the front of the rear section, the end that has the sliding joint, which is also slimmer than the M47.
I bought the M46 together with the correct prop, knowing there were variations, and I wanted the whole set.
(I do still want it, BTW. I still dream of converting my present 240 with the M47 to the old overdrive.
)