well, im pretty sure there were a total of 0 silvia's/180sx's that came with cruise control in Japan so you will either have to fabricate your own throttle control wheel thing or find a way to use the one off your KA.
power steering lines should bolt up to the SR pump
the KA A/C compressor will bolt on to the SR20 (only 2 of the bolts will fit)
have fun
-matt