Can a 3" DP wield up to a 2.5" cat? Probably a dumb question but just wondering if its doable. I'm looking at this.

http://hoganperformance.com/DP8S.htm

The 97 LSS and the 97 Bonneville show to take the same downpipe number in the GM parts dept books. This should be a direct bolt on for your car. A call to your local GM parts department should confirm this.

Nope, stock downpipe is 2.5 outlet, he need to fit a 3 inch outlet to a 2.5 inch cat.

This can be done by any good exhaust shop. I got mine custom made for my Bonneville, a while ago now.

3 inch downpipe/3 inch outlet cat to 2.5 exhaust.

Yes, the 2.5" cat can be welded up to the 3" DP using a 'reducer'. Included in the install if you opt for the one below.

Alex exhaust now has 3" mandrel bent DP'* for W-bodies.
They can do one for our H-bodies, but I need to get the DP off my 93 parts car so they can use it for fabbing up a new 3" one.
The price they quoted me for the 3" mandrel bent SS with flex coupler and 3" flange is $165 installed.

It will be 2 weeks before I can get my DP to them, and it'll be a one week turnaround time before they have them stocked.
If you can wait that long their phone # is 320-763-5574 if you want to setup an appointment.
If you go send me a PM and hopefully we can meet up.

I think there is some misunderstanding here, possibily on my part. The factory downpipe on the 97-03 Bonneville and 97-99 LSS is the same. 2 bolt flange at the top of the downpipe and 4 bolt flange at the bottom. 96 and earlier there are at least 2 different versions that I am aware of at this point. If you have a factory cat on your LSS this pipe will fit. If you have an aftermarket 2.50 cat welded on your downpipe and the flanges at the cat and the rear of the downpipe have been removed I can supply you with an additional flange with a 2.50 nipple welded into it that your cat will clamp to. This link and application chart will show you that the cat is the same on both the Bonny and the LSS.
http://www.car-sound.com/catalog/dir...spx?PartID=186
The outlet of your factory cat is in fact 2.50 but the inlet, if still factory flanged on the 97 and newer 3.8 models is the 4 bolt style and our downpipe will bolt up with no issues.