I just did this adjustment on my 284. I'd think your 2420 would be about the same.
Here's a link to a general how-to:
John's Jinma Tractor Clutch Adjustment
Here's a link to another, with detailed photos:
Keno Tractors Clutch Adjustment PDF
The PTO adjustment on my clutch was extremely sensitive -- I only needed to turn the adjusting nuts about one flat (1/6 of a turn) in order to get it dialed in. Turn too far one way and the PTO clutch slips; too far the other way and it grinds. I had the clutch serviced at a tractor dealer about 10 years ago and they experienced the exact same sensitivity while testing the PTO on a dyno.
Good luck with it,