To even *attempt* to make it legal (which is highly unlikely to be successful without significant, potentially cost-prohibitive modifications), you'd need far more than just a few emission components. You'd essentially need to rebuild a substantial portion of the engine's management system. This would include, at minimum:
* Electronic Fuel Injection (EFI): 1974 Corvettes likely had a carburetor. 1986 required EFI for proper air/fuel mixture control and emissions management. A complete EFI system (intake manifold, injectors, fuel pump, computer, sensors) is needed. This is a major undertaking.
* Electronic Ignition: While a 1974 engine might have electronic ignition, the system would likely need an upgrade to meet 1986's stricter timing and control demands. A new distributor or ignition module might be necessary.
* Catalytic Converter: This is mandatory. A 1974 engine didn't have one, and you'll need one compatible with the EFI system and the exhaust system.
* Oxygen Sensor: This sensor monitors exhaust oxygen levels and is crucial for the EFI system to adjust the air/fuel mixture for optimal emissions.
* EGR (Exhaust Gas Recirculation) System: This recycles some exhaust gases back into the intake to lower combustion temperatures and reduce NOx emissions. A 1974 engine might have a rudimentary system, but it would likely be insufficient for 1986 standards.
* Air Injection System (Possibly): Some 1986 vehicles employed air injection systems to further reduce emissions. Whether this was required for all 1986 vehicles in Missouri depends on the specific model and regulations.
* Properly Calibrated Engine Control Unit (ECU): This is the "brain" of the EFI system. A correctly programmed ECU for your specific engine configuration is essential, and its programming would need to meet 1986 requirements.
The Bottom Line: It's far more practical and cost-effective to find a 1986 or later engine that already complies with emissions standards. Attempting to retrofit a 1974 engine is a massive, likely unsuccessful, and expensive project that would probably violate various emissions regulations. Check with your local Missouri DMV or emissions testing station for specific requirements before undertaking any work. They'll likely tell you it's not feasible.
