Hi Randy,
You asked specifically about the Bachmann skeleton log cars and if they were prototypical in the way they look. The short answer is no.
They ride to high, the bunks are incorrect, the chains are wrong, the wheels are way out of scale and really show, the car is way too short even in 1:22 scale and they lack correct detail. These are the reasons they are relatively inexpensive when you compare them to cars made by Accu-Craft, Hartford, and others.
Can you make good looking usable cars from them? Certainly. Extend the reach, change the bunks, get some good scale wheels, use KD #1 knuckles or L&P’s, do some painting and weathering and you have a very presentable car.
There is no firm date lines in the history of use but generally speaking the disconnected trucks were mainly used in the very early days of rail logging, say 1880’s to 1900’s. The Skeleton log car came into more general use as the locomotive size increased so larger loads could be hauled. Open flat cars probably hauled more log loads than the skeletons and disconnects combined.
A skeleton log car of around 1900-1910 vintage built by say, Russel Wheel and Foundry, would run a load capacity of 60-80 thousand pounds, have a sill length of 34-42 feet and bunk centers of 23-33 feet 10 foot wide bunks and 33 inch wheels. These numbers are of course for standard gauge cars narrow gauge would be smaller and lighter.
You didn’t say what scale your locomotives are or what your railroad is built to but if your after 1:20 scale disconnects look at Accu-Craft and LGB. For 1:20 scale skeletons look at Accu-Craft and of course flats in 1:20 are made by Bachmann and Accu-Craft.
Most saw logs were bucked into 16 or 32 foot lengths in the woods, add 3-4 inches for each 16 foot increment, so the log cars were sized accordingly. There were of course specialty lengths hauled out for things like ship masts, piles, or telephone pols and the old disconnects came in handy for these hauls. They would use extra long rooster pols or just a chain connection between the trucks
or nothing at all.
Well all the above is just my opinion of course,
good luck on your project.
Rick