Yes they were interesting cars and still being used for track work in 1999 and probably much later.
They were originally PC&F cars built in the 1920's.
I think PC&F advertised them in the logging magazines of the time.
I seem to remember John Henderson thought the Shelton shops may have rebuilt some,
and certainly the braking system looks more modern than 1925.
I have some more photos and a few are attached.
#1 was working with the ballast plow in 1989.
I did not measure these cars but I think they are probably 36'.
I know there have been a few articles on them.
One I could find quickly today was in "TimberTimes" issue 18 of January 1998.
This has more photos of a Weyerhaeuser example found near Klamath Falls.
The drawing in TimberTimes shows similar cars to be 36 feet.
I also just looked up my copy of the "Logging Modelers Handbook",
and there is a Pacific Lumber Co version with an overall length of just under 36 foot.
I looked through a few more sources on the PC&F ballast cars,
and now I think they were 34 feet over the frames and maybe 36 feet over the couplings.
I also found a few more photos.
This is from the Ivan Ergish collection that John Henderson held and is one of a number he copied for me after our trip in 1999.
This is at Headquarters Idaho on the Clearwater operations of Potlatch.
Note the hopper sides have been replaced with wood planks.
This is a John Henderson photo from Weyerhaeuser Longview operations.
It seems to be a steel version of the earlier PC&F car.
Whether by them or a rebuild in the Longview shops which were/are capable of such work, I don't know.
However John thought they were supplied by PC&F ( PACCAR)
Don't know for sure what the footboards are for, but in some other photos there appears to be a handrail along the top of the car.
I think therefore they are to allow a crewman to go from car to car,
to open and close the hopper doors, without getting on and off the car while they were moving and dumping ballast.
When I was at Shelton a crew member was doing this and it seemed pretty dangerous.
The ground at Shelton was fairly level so I can see in a typical woods situation it being even more scary.
While as I have suggested Simpson used a ballast plow, Potlatch seemed to use just a baulk of timber attached to one of the cars.
You can see this in the attached photo.