As far as I'm aware, on an '87 4.2L YJ up through '90, the only emissions legal carb in CA is the Carter BBD w/electronic feedback. It was made as a stop-gap measure for Jeep to keep selling the 4.2L engines and still meet emissions requirements, while also finishing and readying the MPFI 4.0L to replace the 4.2L. An O2 sensor detects rich/lean conditions and the computer sends a signal to the stepper motor to adjust the A/F ratio to keep it optimal, in order to reduce emissions. The computer and all the OEM smog equipment must be in place and working to be smog legal here in Cali.
This is the Carter BBD with electronic feedback motor:
Smog laws may vary in CA depending on county, so you'll want to check to see what you are subject to. With that said, some people manage to find the right shop to take their non-legal 4.2L (nuttered and/or aftermarket carb) to and still pass smog.
Any engine mods must be CARB approved, or you risk being fined or just not being able to get smogged. Other than the OEM computer controlled Carter BBD, our only other smog legal options for fuel delivery for the 4.2L in CA are: Howell TBI kit, Mopar MPFI kit, or just an outright engine swap to a newer model fuel injected engine (such as the 4.0L found in newer Wranglers)