Blake, don't take this the wrong way...because you are correct, but he asked if "Anyone ever used a 90mm mas on a 2002 gt??" not if it was a good idea to do at this point in his mods
The stock is an 80mm and will support some HP with out giving troubles...like pegging the MAF. Only time I deem it necessary to replace a MAF is when it becomes pegged or is the cause of a restriction.
Warmest Regards,