use your Si harness and just transfer it over to the GSR motor
you will need:
B series motor mounts
B series shift linkage
B series rear tranny mount bracket
GSR throttle cable with firewall support bracket
GSR axles and half shaft
obd1 GSR ecu
wouldnt hurt to upgrade to a dual core radiator, or a teg radiator.
also need to add a couple wires to your ecu plug
only wire you will need to lengthen will be the O2 Sensor wire.