Take out the thin wire snap ring around the 540 pto shaft, undo the castle nut and pull out the shaft.
Then go round to the right side of the tractor and under the front of the cab you will find a flat plate with 2 bolts that take a 13 mm spanner on the side of the clutch housing. Remove these and underneath will be a similar shaft to the one you took out of the back but with 16 splines and a hole in the end. swap these shafts and you will have 1000rpm PTO. If you want 1000 rpm with the 8 spline shaft then don't remove the back shaft. simply take out the front one and fill the hole in the end with a stack of washers that is 10mm thick and replace.