It sounds like you might have a power beyond type by-pass in there. I'll read up in my shop manual and see what I can figure out. I almost left the A and B series 1800 ad 1900 off the list in the article, as they are different in areas, but they do have the interlock bleed screws and the restrictor valves. 

The power beyond port was used to add an external valve onto one of these tractors. On the C series on, there was a plug you have to remove internally to remove that power beyond setup. I'm something similar has to be done with the A and Bs.
Either way, the interlock bleed screw should not affect whether the 3 point works or not.