Hello Tor, nice to see another Norwegian here. I´ve done history research on quite a few of my older vehicles, and in this case, two things work against you: The fact that your car is a 1968, for which the Cadillac archives don´t have the build sheet copies anymore, and that it is a Califorina car, as the California DMV doesn´t keep their title records for very long. I´ve been thru that myself with a 1975 Lincoln I have, only the last owner title was on file even though the car wasn´t exported to Norway until 2005.
Oh well, there are quite a few ways to try and work around the problems, and I may be able to give you a few tips. However I am packed with work this week, but mail me or call me up next week end, my cell is +47 90 55 67 20, and I´ll try to help you. Snakkes da / talk to you later...
Regards, Tore
Norway
64 Eldo Conv
76 Eldo Conv
78 Sev Ele
80 FBd´E