It will work.

The harness for the Auto model has additional wires going to the Automatic Gearbox Computer. You see this in the S13 Factory Workshop Manual (available in PDF on the net). This isn't an issue. If you wanted to run an auto from a manual loom..Things would be very different.

I had a chopped loom from a S13 Auto, and had to rebuild most of it to get mine working originally. But I've run automatic ECUs and manual ECUs and found very little difference between the 2. I've heard that the Manual ECU has more aggressive timing maps, but that could be just a rumour. It wouldn't make that much difference, Getting the ECU rechipped is a good idea anyway. If you get a bigger turbo, and Z32 AFM, then you'd need a re-chip anyway. As for getting it working good enough..no issues.

Make sure that you get the gearbox-engine plates to suit a CA18, because I think that the Auto and Manual gearboxes have slightly different bellhousings (Not 100% on this).

But for a cruiser..using the Automatic gearbox would be pretty cool. Although I'm not sure it would fit neatly in a 1200 tunnel. I think the CA18 Auto gearboxes are huge.

Chris