This thread is an EXCELLENT read for swapping a 5-speed tranny into your S13 auto. The thread is written for a convertible, but will work for any automatic-transmission S13.

Bonuses - it covers the wiring for getting the key out, getting the car to start, and getting the reverse lights to work.

It even has pictures...

http://forums.nicoclub.com/zerothread?id=77784

Another good one is the www.srswap.com site. Same basic info but it's a little easier for the key issue.