SLP X-pipe...can I use a different brand of cats?

I won an auction for a catted SLP X-pipe for a 98 Cobra on Ebay. They sent me a shorty pipe instead. I was pissed off and they ended up refunding my money and letting me keep the pipe. Now I need cats and the tubes in front of the cats. Do I have to use SLP cats or can I get something like the Magnaflows? I'm going to need the tube in front of the cats either way. The SLP cats are $200 on their site, which is a bit ludicrous, considering I paid $300 for the pipe, shipped. Do I have any other options? What if I took it to an exhaust shop, do you think I could get the rest fabbed up and installed for less than $300?

screw this, I called SLP and it would be about $410 for me to get the parts that I don't have, which is ridiculous. I'll just get a UPR pipe.

I already slapped on a UPR pipe. The installer at the muffler shop said it was one of the better fitting pipes he's installed.