Those measurements are on a new, tight machine. You most likely have worn linkages meaning the clutch levers will travel more distance to achieve the same result. At some point, the wear can be great enough that adjustment cannot be made effectively - you can go for fully disengaged but then slipping, or fully engaged but not disengaging (enough).
For bleeding, start at the source (the tank) and work your way forward methodically. Then go back and check again. If you have any new air after bleeding, then you have a leak somewhere. If it's between the tank and the fuel transfer pump, then you'll likely see the leak externally. If it's between the transfer pump and the injection pumps, then you might have worn components and leaking o-rings (usual reason on old tractors is that the seals lose elasticity and no longer effectively seal). Leaks after the injection pumps would be evident, other than if you have a defective injection valve that lets combustion pressure back into the injection lines - not that uncommon. So work though methodically until you identify the problem.