Steve, I also had to do the "emissions thing" for rego, but here in Oz (NSW) the RTA had a test setup on a dyno that involved following a pre-set drive cycle for about 3 mins. A giant sniffer at the back cought all the xhaust gases (& in my first run, all the unburnt HC that was leaking out faulty filler cap necks). Unfortunately, the RTA's standards are expressed in gm/km as measured over the test, & this does not translate into the % figures that you are looking at.
However, in relation to your questions on CATS & the exhaust system, perhaps the attached pic of my functional (ugly) initial setup will help.
I was advised early on that there was no way a carb engine would pass, CATS or no CATS, so EFI was the only choice - & CATs would be mandatory. The pic shows the CAT & muffler setup that got us through (just) - the O2 sensors are located in the collectors, just in front of the flanges, & point down/out at 45deg.
With the big loop-back exhaust system, we were able to get reliable & realistic readings from the wide-band O2 sensors - she stayed in closed loop all the time.
(It even passed the noise tests - but not without the help of half a dozen s/s pot-scrubbers up each tail-pipe) !
Conventional wisdom here in Oz said that we would never get an 8-stack to pass, but my engineer had other ideas ! He matched specs for the AFR heads, cam & injectors to get what he wanted, then told me that the injectors had to be mounted inboard (like the TWM setup) so that they pointed straight into the ports. It was a challenge, but it all worked in the end - after 5 attempts on the RTA test cell, we finally just scraped through.
BTW, the induction trumpets also had big oil-soaked filter socks on to cut out any HC from spit-backs going into the sniffer.
I started out with a real mind-set against EFI, but I was forced to go that route - I am now so glad I did ! The ease of tuning, the brilliant diagnostics, the reliability - all good stuff !
Sorry I couldn't help with the emissions levels, but maybe the exhaust setup will be useful.
Kind Regards,
Peter D.