(a) For the purpose of determining the classification of felony offenses in title 39 committed prior to November 1, 1989, the following classifications shall be used:
(b) These classifications shall be used for sentencing after November 1, 1989, if the offense was committed on or after July 1, 1982, and prior to November 1, 1989, except first degree murder, which shall be punished by death or life imprisonment.