You could use them, but not the tail pipes, you would have to put turn downs on the mufflers. I have a set I could let go for cheap too if anyone is interested, they would fit Tbirds with IRS too. You couldn't use the tail pipes on a non IRS car. They are just 2 1/4 pipes, same as GT takeoffs, mine are from an 03 Cobra, only have like 4K miles on them. Another thing, not sure how you would go about hanging them up, the hangers on the Cobra system are on the tailpipes, you could probably rig something or get a muffler shop to rig something up though.
Yep, all have 2 1/4, they wish they came with 2 1/2" piping. The 03s get a big hp boost just by going to 2 1/2 inch pipes and modified intakes I hear. The one I did the swap with had an offroad H and stock catback, you should have heard it with my Magnaflow 2 1/2 inch system on it, I could hear him coming like a block away!