Got it running last night, it's definitely loud, our mechanic that does our WOFs said he'll allow it, as in the particular rev range that it's tested at, it's surprisingly quiet.
Oddly enough, it didn't throw any CEL's either for the air injection pump being removed, or the lack of any Cat's. I've removed the codes anyway.
It's not happy by any means, under any load it appears to be cutting spark, and back-firing around 3500 RPM in 2nd, but am told something along these lines is expected with the free'er flowing exhaust and intake.