a 99 gsr ecu wont' have the immobilizer, that or an LS ecu should work fine.

Remember though, OBD2 is going to be looking for a 2ndary O2 sensor, and the whole EGR system. If it doesn't see this functioning it will throw codes that will fail your ass. Also little trick, wait in the parking lot for 5+ minutes with the ecu unplugged, or with the engine ecu fuse pulled, let any residual codes clear out, plug it back up and get tested immediately, it might take a couple minutes for codes to show back up.

Do you have options for who you get to go to. Go to the place with the DUMBEST ppl possible, with the OBD1 computer. They'll plug in, it'll fail horrible, and hopefully, they'll just put your ass on the sniffer.... I have actually heard that this is protocol in some testing facilities.

-PHiZ