I'm curious. Is the gear box the guy in the photo is turning the cable for the boom angle? The one I used had a 2 to 1 reduction on each drum, one for lift, the other boom angle You could reel in or out direct by moving the crank to the drum and the shaft right behind each drum was the little gear for the reduction. We always placed the crane so we didn't have raise or lower the boom while working with it. Lifting loads using the reduction gear and having the cable doubled up using a snatch block made for easy lifting. The Fairmont brake for the lift cable was something I considered sketchy, and I liked to use the crank to lower any load. I suppose the brake may have been there for when someone was running cable out under no load and the drum ratchet was off, but I think that would make a snarly mess of the cable if given a slight chance. We picked up a lot of scrap rail and frogs with it that were never to far away from the track.
Those rail clamps, if adjusted right, will hold more than the boom is capable of lifting. Of course, we had the advantage of wider and slightly heavier track, so erring to side of caution by tying off to a tree seems prudent.