PB Blaster (or equivalent; not WD-40), patience, heat, and brand new allen keys have given me success:
1. remove everything in your way of accessing the front PTO
2. manually clean the three set screw holes with a fine pick. Do not use lubricant if possible.
3. test that brand new allen key gets a great positive lock on set screw.
4. soak each hole for 24-48 hrs. with PB Blaster. (This might take a week as you cannot soak all three at once...)
5. drain penetrant; position 1st hole at 12:00
5. apply heat (small propane torch worked OK for me) to the bottom of the pulley groove, towards the back, inline with set screw hole
6. put on work gloves, get positive lock with allen key, start coaxing set screw out. Add a little penetrant as you do this.
If the above does not work; you probably will have to drill them out... :-( You'll need patience, high quality bits, slow speed, steady hand, and cutting fluid.
There are 2 set screws per hole; the top one is usually dirty, but the bottom usually remains clean.
If the allen key starts to wear/round, use another new one.
That will get the PTO clutch off. Remaining are the clutch bearing and basket pulley. The latter are usually not as difficult to get off, but not painless either.
Hope this helps,