Your engine swap is fine for California except while installing the 1995 Chevy 350, you will need to install all the emission components for that engine as well, including ONLY the Catalytic Converter which it came equipped with; which in this case is a Federal CAT. In California, after an engine swap such as this is complete, the vehicle will have to be inspected by a California State Smog Check Referee. The Referee will ensure that the job was done properly and that the new engine does not pollute. If all is well they will issue you a BAR label which will be placed somewhere on your vehicles chassis which will be an indication that the vehicle is California legal.
In this case, since you will be moving to California, your 1989 Chevy Astro van will need to have its first smog inspection performed by a State Smog Check Referee. You can contact the referee by calling (800)622-7733.
