Martin,you are correct! Earl has some very good WSL photos.
Caboose 4 was one of two "short" cabooses that the WS made. However, at some time after this caboose was built, the WS shops built a second caboose 4 which was a "long" caboose with dimensions similar to most other WS cabooses. When long caboose 4 came into service, short caboose 4 was renumbered 6, which has been discussed on this forum.
Currently, I am in Grass Valley, CA. I have been at the Nevada County Narrow Gauge Museum in Nevada City earlier this afternoon, visiting with John Christensen. The only part of Caboose 6, formerly no. 4,that is on the property is its cupola. John showed it to me. I handled it and its cupola windows. Earl still has the rest of the caboose but it will be moved to the Museum when needed.
Right now,John is restoring trucks for the to be restored F&CC coach which has been at the Museum for several years.
John has his hands full with restorations but it sure is nice to see so many restored WS cars!
Best regards, Hart Corbett