I've had the same problem with my TED20; unfortunately the original PTO guards were fairly small and not designed to accommodate an o/r clutch adaptor. I've heard, but not yet tried, that the MF35 guard will fit as they have the same mounting hole centres (can Stufe35 confirm?) so that may be worth a look, as I believe they are bit bigger.
Adding an extension to the original guard might be feasible but it needs to be made of at least 1/8" or 3mm steel sheet and that's not easily bent up without suitable tooling/heat.
It might be worth a talk to your local ag engineers to see if they can suggest one from another tractor.
I've not found any problem with my o/r adaptor fouling the pickup hitch.