Orrrr ya could just pick up the parts you need to connect it .....ahead of time.
The headers you have in your hand, so finding out if it's 3inch OD or ID is really easy. You likely can't find a reducer to the stock 2.25inch size pipe from a 3". Some exhaust shops will make one for you super cheap. But that's a large difference. Another idea is to get two adapters. From 3 to 2.5, then 2.5 to 2.25. A couple of clamps and some planning and it'll be fine until you get a different catback or have more work done.
One of the three installs the other week had this issue. An extra 30 min of parts hunting and it was cleared up.
