what would happen if........

late model resto is sold out of egr kit, but that is the cheapest i have seen it

The part number M12071N-302 has been replaced in 2008, and the new part M-12071-L302 is wayyy too expensive. Some other Mustang specality stores may still have it available.
 
go to the junk yard and grap one! its not to hard to get them.
put it on ur car, hook it and everything, start the car, pull the vacuum
hose off of it, plug the the lil vacuum line. using a hand vacuum pump, put it on the egr .pump it up , the car should die or stumble, if it does! the egr is working correctly
nothing to do