Cool.
Let me try to answer your original question.
For ease of explanation, here is a diagram of a max torque clutch:
The bushing #3 rides between the sleeve #12 and the sprocket #2
In order to replace the bushing with a bearing it would have to be the same size dimensionally as the bushing. One thing you could try - is take apart the clutch and bring the bushing in to a Motion Industries (formerly Bearings and Drives) or maybe even a Fastenal and see if they can match up a bearing to the bushing. Probably a needle style bearing as you suggested as most ball bearings would be wider than the space allows (the article you posted makes it look like there might be options with roller bearings though).
I'm not sure I buy the whole heat failure argument if they are kept oiled with a heavy weight 80-90 gear oil or even lithium grease it should stay fairly well lubricated and cool. Debris is another matter - and oils and grease attract debris so that may be true. I just can't imaging that a needle bearing can handle 8500 rpm on a two stroke piston wrist pin at 200+ degrees but fail at 3600 rpm in a 4 stroke PTO. I'm no expert though so perhaps I am missing something.
As others have suggested you could make the space between the sleeve wider by using a smaller sleeve or a larger diameter sprocket but the work it would take would hardly be worth the effort.