I think I can handle this one, Dave my parts are in the same boat.

The Cat situation :
will require you to have a shop or yourself if your capable to cut the monolith from your solo cat and weld it into place using dave's catless dp as parts.

HPT: If your going to go hotroddin' your car you should own your own copy of HPT pro. That way you can flash dave's tune as a starter, keep your stock tune in a safe place , and have the capability to use the scanner to log any issues you may be having with your tune (KR, lean boost cutback ,etc)
You can post your scan's up when you get into trouble and have a pro take a look. Then suggest some changes.