I agree with ronald. Any 'man' can put a 1200 gearbox on. The gearbox wont break your ribs if you rest it ontop of your chest during 'jiggles'.

The same is not true for a CA18 gearbox..I tried, and I almost broke a rib

Especially the A-seres, they can be leaned back a bit on the engine mounts, making gearbox fitment, quite easy.

It's easily possible to put an a12+box in, but you will very likely scratch up the firewall or front panel.

Do it in 2 steps.