These creatures have been around for a long time. Called a 'Cary-Lift', they are designed so the lifting mechanism can be set on the 'front' of the machine so if you have to drive around it won't flop all over. It will lift about 14 feet high and since the whole lifting yoke can be moved forward and back (the vertical part moves about 4 feet via cylinders just inside the rear tires), you can move the teeth forward and backwards. this model had a top clamp and kickers for log handling, but the teeth were basic forklift teeth so the machine could be used for lumber bundles as well if the top clamp were removed. The vintage of this machine was early 1960's, and it featured a Detroit 3-71 engine. (a two valve standard Detroit). It had an Allison powershift transmission. It was steered on both axles with an axle of Pettibone design.
These machines appear of this design in multiple sizes ranging from smaller 6,000 lb models, and I have even read of 60,000 lb monsters. This one was a 'Super 15' of an older style, implying that its lifting capacity was 15,000 lbs. Older models had gas engines. This model used the operator compartment as sort of a guide to keep the arms in alignment with a couple of inches of slack so the overhead could bang back and forth to the left and right. Later models had an overhead that was smaller and did not need to bang on the cab for stability.
A perennial problem with these machines were the brakes. They had hydrovac assisted hydraulic brakes which didn't seem to be up to the task. Shoes would disintegrate and the like. We bought a brake retrofit kit for ours which helped a lot. Now log handling is commonly done with standard front end loaders with log forks, but in the 1960's such machines were not common and hence these dedicated but special purpose forklifts were in many mills. As of this writing in 2005, Pettibone Cary-Lifts were still in production. We bought ours out of a sawmill and used it around for a good number of years before selling it off. You really need flat ground to work a machine like this, and not all places where trees grow are flat which is the real drawback of using a forklift to load logs.
It looks sort of clutsy, but was actually fairly nimble and with steering on both ends turned on a quite short radius. Much shorter, I might say, than the steered front end loaders of the day which were typically steered only on the rear axle. We even acquired a buck for the thing and used it sparingly to load rock. I say sparingly as the Rzeppa joints in the steering knuckles were very expensive and we didn't want to risk breaking one. they were not just an axle with a universal joint, but rather used a very complex (and in lots of parts) joint that was designed to be a constant velocity joint.