These are the tips I used, although I think 4" would fit just fine. At the time I just wasn't sure:
Exhaust Tip 2.50" Inlet Dual 3.50 X 9.00 Long Round WDWDRS3500950-250-HP-SS Double Wall Polished 304 Stainless Wesdon Exhaust Tip.
One thing I noticed before purchase was the weight -- 4 lbs. each, heavy and solid feeling. I had them welded on by an independent garage that does custom exhaust and they were also impressed by the quality. They cut off about 10 inches of existing pipe before welding on new stainless, and the original hangers were cut off and reused. Total cost was 130.00 plus the cost of the tips.