Despite what is printed on the ticket, those 1991 tickets do include AK. But you must have them converted to the current magnetic strip tickets at Guest Relations (no charge for this) before they can be used. You may enter any of the four theme parks with this new ticket.
You used to be able to apply the dollar value of the two unused days towards a new ticket but Disney changed that policy on January 1, 2006. Your only option now is to use up the remainng days from that old ticket.