Just as a precaution I'd always fit an over-run coupler when using a topper on a TE20, particularly. Without it you acn find that coming to the end of a run, slowing down the tractor, then finding that the rotating topper blade is trying to drive back through the pto pushing the tractor forward; particularly unnerving if you're working down slope. The overrun coupler will eliminate that.
I don't know what sort of ground you're working over but if it's rocky or there are large clumps that might stop topper blade/pto shaft rotation you risk clutch damage on the Fergie. If that's the case then it's worth fitting a slip clutch at the topper end of the pto shaft to avoid it. Your local ag engineers will be able to advise or you can find one by web search.