do i really need 3" exhaust

Oldmanrick, owning an early abody creates issues on parts availability. Headers for this body style by any manufacturer that I have found are all step headers using 1 5/8 - 1 3/4 step. That is probably another reason I ask if 3" is over kill on the system. Pricing between 2 1/2 and 3" is probably only $20 for x or h pipes. My concern is if 3" isn't needed I can tuck a 2 1/2 pipe under body for cleance of trans mount which has to be altered and road clearance. Also because I moved springs in I am probably going to have to bring exhaust out in frt of rear tires as there's no room at fuel tank and frame. Mopekid brings up a good point on using a dump for when I race.
Thanks Rod