Confusing...
You first said your car was a GSR (P72), yet why do you have an LS wiring harness...

Did I miss something here? Or do you have an LS with a GSR swap?? I just don't understand your post, why would you have a B16 in a GSR?? Unless your motor was toast and you replaced it with a relatively cheaper and easier to find B16.

No I don't believe the purge solenoid would cause gas to spit out of the exhaust. Obviously the gas comes from your injectors, one (or all) of which may be being held open for too long.

Is there a short to ground or other symptom that would cause the injector to constantly spray gas? Better fix it soon, gas prices keep goin up n up n up.