[jhv48]

You will NOT be able to LEGALLY transfer the Montana registration to California. The reason is that your car is NOT a 1965 vehicle (it was not built in 1965). California considers this fraud if you transfer the title to a 1965 California title.
Thus, you will need to register it using the sb100 route. Lots of hoops to jump through but it can be done.
The first thing I would do is visit the dmv and talk to a supervisor about bringing in a completed kit car with a 1965 Montana title. Find one who knows their stuff or you’ll get the runaround. If they convince you it can be done, Then and only then would I buy the car.