* Emissions Standards: California has significantly stricter emissions standards than the rest of the US. Engines from that era, even if new crate engines, would not meet those standards. The 1986 S-10 would have had specific emissions equipment designed for its original engine, and a replacement engine, even a similar displacement, wouldn't automatically have the same emissions controls.
* CARB Compliance: To be legal in California, an engine swap needs to be CARB (California Air Resources Board) compliant. This means it needs to have a CARB Executive Order (EO) number showing it meets California's emissions regulations. A 1982-86 3.4L crate engine almost certainly does *not* have a CARB EO.
* Matching Components: Even if you found a miraculously CARB-compliant 3.4L engine from that era, you'd likely struggle to find all the necessary compliant components (fuel injection, catalytic converter, etc.) that would work correctly with the engine and be accepted by the smog inspector.
* Engine Management System: The engine management system (computer, sensors, etc.) would need to be compatible with California emissions standards. This would be incredibly difficult to achieve with a crate engine from that generation.
In short, while mechanically feasible, the swap is highly improbable to pass smog. You would be far better off rebuilding or replacing the original engine with a similarly-aged engine that is known to be compatible and pass the California smog test. Even then, finding an engine in good enough condition to meet the requirements might be challenging.
