Reuse the shift stick bracket from the Z32 gearbox. You have to cut out some small triangles from it, bend it to a Z-shape to fit the S13 under body and then weld the cut outs together. (borrowed picture)
The new short shift
A small change of shift stick position compared to the original (borrowed picture)
A plate to cover the hole at the shift stick (borrowed picture)
A bracket to hold the gearbox in place (borrowed picture)
Aligning the gearbox with the rear axle. Put a steel tube in the gearbox, aim it towards the centre of the rear axle flange and find the final position of the gearbox bracket. (borrowed picture)
Side view (borrowed picture)
Front view (borrowed picture)
The prop shaft. Mount the Z32 yoke in the gearbox and the original flange on the rear axle. Measure the centre distance between the loops in the yoke and in the rear flange. Use this measure and go to your local prop shaft supplier and have him to make your new prop shaft. The shaft rotate at about 10.000rpm at max speed so it has to be dimensioned for the forced and also balanced.
(I will edit this post and put in a better photo and necessary dimensions)