[hthorn]

You can either bypass the CAT or use the gauge--my guess is your neighbors will appreciate it more if you use the gauge! It will tell you definitively. Much simpler. Maybe once before you do the ignition work, and once after. Then after the exhaust work is completed, you should be able to feel the difference. But if you can find your earplugs, and not your vacuum gauge...
Black smoke could mean incomplete combustion, i.e. unburned fuel, which makes it now 99% likely that your CAT is defective.
...Auxilary vacuum pump? Not unless you have a diesel. You might want to check your master cylinder. Low vacuum would cause a "hard pedal". Also, if you're not bleeding the system properly, you might not be getting all the air out.