I had much the same problem with the exact same type of shield except for the fact that I wasn't 't even able to replace the shear bolt on my blower. Now one thing was for sure and that was i wasn't about to be monkeying around with this shield in the middle of winter, probably in the middle of the night in a snow storm, so this fall before the snow hit I deftly removed the offending shield using a hammer and chisel. Came off in three not so neat pieces, end of problem, now I can grease the u joints and replace the shear bolt if necessary without getting, Yuh know all snarly and careless.
Now before the workplace health and safety people chime in about the inherent dangers of doing this. Firstly I'm not telling anyone to do the same and I know enough about P.T.O's and how dangerous they can be to shut off the engine before getting anywhere close to them as they can and will kill.