Help 900ss Desmo

New to this forum, but after some assistance from people who know.
A friend has died at 56 years leaving behind a Ducati. His wife needs to sell it, I need help valuing and direction.
The bike is a 1982, 1 owner 900ss Desmo blue and silver, alloy wheels, tatty and poor condition. Stored since I believe 1988, with the rear cylinder head removed, believed vavle guide problem. The bike is all complete minus a couple of cables and two vavles with approx 30,000 miles on the clock. In need of restoration but very complete with new clutch. The engine will turn over freely and very smoothly.
Any thoughts and guidance would be very much appreciated. I could probably upload a picture or provide more information if needed.
Thanks in advance.