Ron,
The only photos I've seen are from Datafile 144 and 145 Caproni Ca.3 At War vol.1-2. One shows wooden leather covered seats mounted in a reproduction Ca.3. The second photo is from a restored post war Ca.3 with shallow wooden leather covered seats with the forward section of the fuselage fuel tanks serving as the seat backs. These metal seat backs judging from their dish shape are to allow the flight grew to wear the rather bulky Italian parachute pack . I wish I could be of more help my old friend and your Ca.3 project is awesome.
Highest Regards,
Gregory Jouette