In the process of replacing my rusted-out lower cat, I broke off both of the bolts that connected it to the upper cat. I then proceeded to attempt to remove the upper cat by Dremeling off the three nuts used to connect it cylinder head, and now I'm not able to remove the upper cat from the cylinder head. The three studs are still in place and there appears to be a lot rust between the studs and the flange. I sprayed PB Blaster on the studs and flange several time over the past week and still can't get the upper cat to budge. Any suggestions on what to do now would be appreciated.