a buddy of mine is driving an elco that sat for that long. if i recall he just ran the tank down and topped it off. anyways if it was my three year parked resurrection ,and the tank was low, id drain it for the sake of trying to make it run as good as possible. nobody likes hard starts our idling rough, but everyone likes being nice to their z's whenever they can :)
you could always throw the old 91 in your lawnmower or another car that you dont love as much.ha