For the IAB you will need to move A20 to A17. Since you will be using the OBD2 engine harness and an OBD1 GS-R ECU you will need to cut the black wire at the IAB plug and give it a 12V switched source. You can get this from the yel/blk wire at the injectors or the IACV.
The reason this needs to be done is due to the fact that the OBD1 GS-R ECU uses a negative trigger to activate the IAB and the OBD2 GS-R ECU uses a positive trigger to activate the IAB. If you use the OBD2 GS-R engine harness with the OBD1 GS-R ECU the IAB will not work by just moving A20 to A17 (as with an OBD1 GS-R ECU and OBD1 GS-R engine harness).