To fit the 71-series automatic, Datsun fitted a larger tunnel to the auto 1200. You can fit this tunnel to any 1200 rather easily, and it seems to be identical to early B210 and 610 tunnels (pre-catalytic convertor). See Tunnel.

With more torque than a stock A14, it is recommended to fit a larger differential. The H150 can only handle a little more torque. It is recommended to fit an H165 for use with a 2.4 liter, or with a turbo 1.8. They cheap swap is an H190 out of a Datsun 320 pickup, it is however it little narrower than than the 1200 rear axle assembly.