The auto tailshaft is a little longer than the manual tailshaft. I think this is common among all Nissan/Datsuns. As such I would say the manual box is slightly longer. The gearboxes bolt up the same to the engine, but you'll need a custom crossmember, or to modify a standard crossmember if you're doing a conversion. The bolt up in slightly different places.
As for the crossmember, I'm not sure! But I would guess they are?
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green200b - aka Alistair
The fleet:
Australia:
'80 200B GX - the
green200b - hibernating
'81 RX-7 - 12A extend port - daily
'74 RX-2 - 13B bridgeport - cruiser
Europe:
'93 200SX - CA18DET - tourer
Green200B has forgotten more about 200Bs than we will ever know.