I have already done the conversion, but I am getting some vibration. I know the mount is different but I am not sure about the crossmember. The old M47 one fit, but I am wondering if the clearance is too tight. Also do M46 gearboxes normally have spacer washers between it and the frame? The original m47 did not.
I'm not having much luck with gearboxes these days. I have 2 240s and 2 m46s with bad actuator seals, an m47 with a bad input bearing, and an aw70 I can't give away.

the crossmember is the same for all the 240's trannies, aw70/71 and the m45/46/47 the only thign that is different is the mounting of it. On some with new mounts things can get a bit louder. Make sure everything is all tight

Thanks for the info. I thought the crossmember was different between m45 and m46. I recall having to do a little bit of "sledgehammer reshaping" to the crossmember when I converted my 75 245 from a 4 speed to M46.

The cross members are all the same but they bolt into a different set of captive nuts in the chassis, because some boxes are longer than others. The rubber mounts differ, I am not quite sure why, and I have noticed different arrangements of washers under the cross member bolts.
My 93 simply bolts straight on with no rubber spacers at all. My 89 has large rubber pads about 1/4 inch thick between the cross member and the chassis.
I can't think the alignment is significantly different, but I suppose one might be quieter.
Don't forget there is a right and wrong way round for the cross member, because of the S-shaped profile to clear the exhaust pipe.