If I'm not mistaken he's referring to the slipfitter! Regarding the bolts through the top as opposed to the usual clamp where the blots are tightened from the bottom! Thats my guess!
Never saw an OV-15 with carriage bolts like this. Both of mine use 3/8" threaded rods. This is either an early Westinghouse redesign or a very late Crouse-Hinds.