I am not a great believer in the commonly held belief that loggers built most equipment in their own shops.
However there are some good examples of re-purposing equipment to better suit the operations needs.
Simpson's water car is a one example, as is the ballast plow which was built on a PC&F moving car.
I try not to have too many examples of home built stock.
But I have built the water cars and a couple of tank car conversions.
The two shots of the water cars I must think be at Shelton probably as the Peninsula Railway museum tried to get its act together.
The photo of the train with Alco #600 I would guess is taken at the Roots of Motive Power Museum in California,
after Chris Baldo acquired some items of Simpson's equipment.
Alco #600 was used by Simpson as the mill switcher and then was spare lokey for several years.
I saw it as that in 1999.
Attached is a photo from my collection of it working at Shelton.
The water car is in a earlier Simpson livery.
Again from my collection is a photo of this coupled to its pair SW900 #900, one of the few SW900 fitted with dynamic brakes.
Simpson also had another Alco #20 which they got when they brought out Shafer in the early 1950's.
I added a photo of this at Shelton with the Rayonier pulp mill in the background.
Almost out of shot in the photo you posted is one of the 1920's PC&F ballast cars as restored.
These were long lived and the photo I took in 1999 shows it at work spreading ballast near Shelton.