The 2.5 will work - it says on their site that it bolts to any stock or aftermarket catback so you should be fine.
Originally Posted by ZZP
1 3/4" headers can be selected with either 3" or 2.5" downpipe sections but we recommend 3" because the cat flows more. 3" downpipe with bolt in 3" exit should only be selected with our 3" catback system. For custom exhaust systems please select a weld in option for the downpipe exit. 2.5" bolt in option bolts to all stock or aftermarket 2.5" catback systems.
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