IH sickle bar model?

Greetings! Can anybody help me ID what model this mower is? 3-point hitch, 6' bar, pitman arm (missing), says M-2571 on the large drive pulley (best I can make out), 45C375RI on another part (again, best I can make out).
Been scouring the internet looking for photos of various models, but came up empty.

Here's another photo. I've always cut my fields with bush hog, so I have no idea as to what I am looking at here. I know the pitman arm (?) is missing, along with the part that attaches to the "ball" on the bar (socket-type thing?) Any idea where I can get schematics or a manual?

One item I can't see from your photo; on the left an arm pivots at lower link point, one end goes under tractor lower link and other end hooks to actual cutter bar lift, causing bar to lift picking up outer end of bar in advance of inner end. If you can confirm that I think we have it nailed. IH built numerous mowers that have many of the same components, thus one has to get into minor details to be sure on model number.