Rough outline:
Get the car high off the ground. I recommend the Truck/SUV jack stands.
All of the S30's have the same length driveshaft. It fits the auto, 4 speed, and 5 speed.
You will not need a different ecu.
But you will need to bridge the wires on the neutral safety switch.
Just the clutch and brake pedals, the pedal box is the same.
EVERYTHING for the clutch system. You will not need to cut anything for this. there are already mounts in place for the master cylinder.
You will need to cut the shifter hole. Follow the line that's already there. (Once you pull the shifter off you will see what I'm talking about)
Remove the vacuum line that leads to the transmission, and replace the connector on the intake manifold with the manual trans. one. (I prefer this to plugging the open hole)
The pedals are the biggest PITA is my opinion.
Good luck.