Yes, if done correctly, swapping in a GM TBI into an '84 anything, will be CARB (Calif Air Resource Board) legal. You will have to configure the '84 to meet the SMOG requirements of the engine you install. This means every SMOG item in the truck that the TBI came out of, must be installed in the CJ. Also, if the enines out of a 3/4-ton truck, you'll have to configure it as if it came out of a 1/2-ton.
You can choose to configure your TBI to any number of years/configurations; but all items must be from a platform certified to operate in CA. Most critical is to match the ECM/PROM to the engine/trans combo. The Ref will scan the ECM for the PROM ID--it better match the engine configuration you've decided upon.
Details, such as "check engine" light, and the presence of a diagnostic jack are critical to passing; my install almost failed because I used the "Check Emissions" light that came in my '88 XJ, versus a light labeled "check engine"; I was admonished to relabel my light!