OK, this is how I did it:
Note: You need to cut the original gearbox mounts off the tunnel to fit this, so don't change your mind halfway through.
Source and fit the flex plate, oil lines and gearbox from a series 2, R30 Skyline. After the old mounts are gone, these are a straight swap.
You need to fabricate new gearbox mounts. The original cross member is still used, but the mounting foot on the gearbox is smaller, so there is some fiddling.
The gear shifter linkage from the R30 is a straight fit, but I'm sure you could shorten the original one if you had to.
The gearbox output shaft is bigger, so a new/modified tail shaft is required.
I used the front yolk from the R30 shaft, welded to the shortened (24mm?) 280zx shaft.
The guy that did the tail shaft, recommended looking for a VL Commodore or early Navara tail shaft if I need to get another one done, because these have replaceable uni joints. They would still need to be modified though.
The standard front exhaust section no longer fits, because the rear cross member is now about 160mm further back. That got extended and the middle section shortened the same amount. It's not perfect, but it works OK.
Most of the wiring is a straight swap, except for the bits that aren't.
I had to add a relay to get the reversing lights working and of course had to add an overdrive disable switch in the cabin.
Note: There are other gearbox options out there (RX-7), but you would still need the R30 bell housing to make it fit easily.
Pete