Yes, most implements seem to have stated on them not to run them over 540 rpm.
I do cheat however. I use a brush cutter for my land which is flat but agricultural so a grass mower is no good. Given that now all I need to do is cut the top of the grass, rather than running the brush cutter pto in first gear at 2,800 rpm in 4th gear, I use the second pto speed and run the tractor in 5th gear at 1,800 rpm. Roughly the same brushcutter speed with slightlly faster forward movement for less engine revs. this wont work with everything but for my land with my grass, it is ideal. Come spring, it will be back to 4th gear for a while.
I didn't realise you didn't have a tacho on your machine. As a general rule of thumb, run at 2/3 throttle in 1st pto gear and you should be near to 540 pto rpm. You will probably be a bit under the 540 limit which is not a bad thing.
Gary