How big are the stock tail pipes and how restrictive are they?

[96_4.6]

On say my 96 mustang gt the stock tail pipes from the muffler to the rear bumper are 2.25 in. right? If not then they must be 2.5in. cause I think the ones on the 96 cobra appear to be bigger. Also how restrictive are they i.e. I'm sure everyone noticed the huge crimp in the pipes near the gas-tank like someone pinched it in the vice, why is that? Cause my tailpipes have seen better days and I would like then to match the size of my H-pipe and mufflers and the H-pipe is 2.5 in. and I dont like that pinch in the pipe too much and mac sells new ones for like $179 I think, thanks for any input