First off there is nothing from a JD 510 that will fit the JD 535. Maybe a pickup tooth or roller chain but the main parts of the baler are completely different.
The JD 535 could have been either 540 or 1000 PTO. The gearbox gets turned around and then you use the correct PTO for your RPM.
Those complete CV PTO shafts are not cheap. I think they are over $1200.
The Bale track monitor should be easy to find used. I think the 430,435,530, and 535 all used the same box.