Well, the other day I tried to drive it to work. It started having a miss under 2500rpm that would go away above that, so I just kept it revved a little higher. I was worried that it might suffer from the dreaded "loose timing pulley bolt" syndrome with a wallowed-out keyway on the crank. Then the next trip, the rusted exhaust seemed to get a little quieter and the miss was there no matter what rpm. I barely made it home, but I was relieved for sure. Tonight I cut a hole in the exhaust pipe right in front of the Cat, and though it was loud, the miss was gone. I guess the cat decided to clog itself off.
No big deal though, I still have the parts rig from Zig and it still has a stock 16v exhaust in good shape in it, so I will just swap it over...