My EFI Blown 435" sniffed at 35ppm HC and .4% CO with an agressive cam. No cats. No EGR. No PCV. No Nothing.
But...it's EFI. You can tune a carb to do this too...but without instrumentation, it's hard. Buy a UEGO wideband system and use it to tune. See
http://www.innovatemotorsports.com for a good one.
Byron