on my twin 496ho set up my starboard engine is idleing about 150-200 more rpms than my port side eng. ? i don't know if it could be the gaffrig gauge or maybe i'll have the mechanic hook up the hand held computer to see. if it checks out that this is true can anything be adj to fix this ?

Stock 496 ECM's are set to have the engine idle about 600 rpms in gear and about 650 rpms out of gear. what are yours idling at? There is no adjustment setting other than the ECM which handles the idle air motor to make the adjustments.
I would also recommend checking your throttle linkage to make sure one is not out of adjustment or binding and holding one throttle open mechanically.
The scan tool would be required beyond that check.
If you guages were correct before chances are its not a guage differential and you should be also able to hear and tell when the engines are idling at that kind of rpm difference.

Best Regards,
Ray @ Raylar