For California Appendix E covers engine changes.
https://www.bar.ca.gov/pdf/Smog_Check_Reference_Guide.pdf
Swap to electric would be easy here but not cheap.
https://www.youtube.com/watch?v=IGjOY4JBmy4
Excellent, that is what CARB/CA DOT goes by. I didn't spend too much time reading it, but I don't see a non-OBD-1/2 compatible diesel (even if brand new) conversion for OBD 1/2 vehicle possible in CA.