USDM is b18c1 JDM is b18c. I would recommend you running your p28 Ecu you currently have in your si. I you want the p72 USDM gs-r ecu we could trade. I have it chipped and upgraded by Erick's Racing. The complete changover must include Motormounts, Shift linkage, Axles, complete engine with tranny, manifold, distributor, and harness. You don't need the ecu
The P28 is the D16Z6' ECU, commonly used in swaps because it is easy to chip to run pretty much any motor. The P72 is the stock GSR ECU, and controls all the normal functions including the IABs. There is no significance over the P72, unless it has been chipped to run a GSR properly.