It's all about the engine types require different bellhousings and also have different cranks. An A series motor (in most B series Datsuns) have interchangeable gearboxes. L series engines for 180Bs etc... wont bolt up. RB Series engines from skylines are not an A series engine and also wont bolt to the back on an A series engine.

Check dd's wiki link is indeed a good idea to get some further understanding of gearboxes.

would a skyline 5 speed bolt up to an a12 or a14?

at the moment is a a15/5speed on ebay item#320067873932 ph#(02)96309534 for sale one bet$99

the B310 5speeds (63series) were overdrive.
check out the link that ddgonzal posted up for you. it has everything you need to know. ie ratios of different series boxes etc.

why not just get another 4speed? theyre good for track work and city driving etc.

youll have a hard time gettin one in toowoomba buddy, you may have to broaden your scope to the whole of australia.
and if you do come across a 5 speed to suit an a series, i hope you have a biiig wad of cash to pay for it.
these gearboxes normally go for between 700-1500 bucks depending on condition.
IF you can find one..

were the datsun b310 boxes over drive or not if not wat 5spd over drive will bolt on an a12 engine and were can i get one in toowoomba

thanks for all you help and info

I dont think you will need to do any mods.

what modds have to be done to attach. will it bolt straight on does a 120y tailshaft fitt in to the back of box and trans tunnel moddin

The box out of a B310 will fit, but a 200B wont.