Here's a couple of pics of the IAT and MAP sensor installations on the S13 SR20DET I'm using for development. This should give you an idea of what's involved with this conversion.
GM IAT sensor. I made a bung on the lathe and welded it on with an oxy/acetylene torch using aluminum welding flux. Not extremely pretty, but it works. The sensor is 3/8 NPT and is wired into the EGR temp. sensor input on the ECU. I used a heat gun and some ice water to calibrate the voltage to temp. conversion table.
GM 3bar MAP sensor takes 5V to operate. I used the TPS 5V supply, but may end up adding a 5V regulator powered from the MAF sensor 12V supply when I remove the MAF and wire the MAP sensor permanently into the MAF input on the ECU. The MAP sensor is currently connected to an analog input on my Calum RTv2. The voltage to pressure relationship is linear so no conversion table is required.
Enjoy,
Dave