You need to cut it either way. The front cat is welded to the down pipe, then bolted to second cat, which is bolted to the rest of exhaust.
I'm not going to weld mine, I'm using a clamp. Cut it, use a pipe expander (loaner tool from autozone), and then clamp it. Then I'm putting a flex pipe in behind that to make up the length difference.
The Magnaflow is quite a bit cheaper than the Dynomax
http://www.jegs.com/webapp/wcs/stor...rect&categoryId=119174&parentCategoryId=10251
Jeg's doesn't carry it, which is why I didn't buy it (was ordering other stuff from them and wanted it to all be one order), but they have an offset version that is cool. It would gain you some ground clearance as the whole cat is to the top side.
I'll post up some pics of mine once the cat gets in. It's a new item for Jegs, and no one told me when I ordered it it would be back ordered for 4 weeks, if they had I would have ordered the offset cat from a different vender.