you really shouldnt have got an S13 auto, as they are fully electronic. you should have, and probably should still go with a bluebird auto like shaun has.
as they are fully hydraulic and they need no wiring to go to them for the engine to run properly or the auto to shift properly. and then you just run a manual CA ecu

you might be able to get an older style speedo sender and put it in where the electronic sender is, then just use your standard speedo cable or a slighty longer one, 120y, 200b etc
but then you might need the speed sensor for it to shift properly
all of the inputs and outputs from the auto to its control unit should be kept, any that dont go to the auto computer or the ecu you probably wont need