Jim
With any bikes I have owned that I felt were worth more than a used sticker price I just get them appraised and goes with insurance companies who deal with such beasts. In the case of a sandcast, being over 40 years the appraisal would be a must to get insurance on it here in Canada.
Insurance companies will say something like this about insuring Vintage motorcycles:
Older bikes, depending on condition, will often need to be appraised before insurance companies can assess proper risk.