... It really is a PITA.
You'll need to have ALL the original emissions-related equipment in place and operating, in addition to passing measured emissions. The cam could be a problem as well, as it will likely affect emissions measurements. Only the Thorley header has CARB exemption.
Petroworks has been successful in getting 1.6L engine transplants to pass a referee, but there is some expense involved. I believe one needs the same or newer year's engine, and then the emissions limits for that later year apply.
I think the cutoff-date for smog is fixed at around 1975.
Edit: The most compelling reason for keeping my Zuk registered & smog-legal (besides driving to the trails) is that those trails that I like to drive require street-legal registration. I do a lot of camping and exploring in National Parks, where street-legal is required.