I just repacked mine last weekend and it was a pia but next time should be a lot easier. I got my barkers exhaust in August of 2010 so I thought it would be blown out by now but I was way wrong.
It still had 90% left but I figured since it's open I mite as well change it. Make sure you get a 3/16" drill bit for stainless steel because regular bits wont work for drilling out the rivets. I wrapped the paking around the core really tight and it slid in the exhaust very easily.
Then you need to squish the exhaust back into an oval because it will become a circle and not be able to fit the cap back on. With the cap back on I riveted the stainless steel rivets with a manual gun which was the most time consuming part. Ofcoarse after I did that I looked down the core and it wasn't lined up with the reverse megaphone inlet.
So time to drill the new rivets out and start all over. I got it lined up perfect this time but had no more rivets since they only give you 6 with the repack kit. So I went to home depot and got a pack of aluminium 3/16" by 1/2" rivets. They were much easier to deal with and i was all done.
Also for those of you who have the aluminium canister and didn't get it in black, get something like a scotch bright pad and go "with the grain" and it will look like you just bought it. This is the video I used to help me through it. Good Luck!