Since you dropped the body swap idea and I believe you said the check engine light is out I assume the issue with smog is the readiness monitors are not setting.
EVAP can be not ready and pass if there are no codes set so that leaves the 02 sensor heater circuit, the EGR and secondary air injection as the items that will prevent passing inspection.
The EGR and the secondary injection are both exhaust related so I would bet a very small exhaust leak is the issue; just enough to keep the monitors from giving the all clear but not enough to set a code and turn on the check engine light.
The 02 heater circuit has to be the sensor, if it was an issue with the harness power a code would be set.
On the plus side non of that stuff matters except for the smog inspectionn, that doesn't help get it registered but it does make your ride a good candidate for someone wanting to LS swap a classic car or pickup