I read your post with great interest, as I also have Dong Feng, and like your father, find that PTO guard to be a nuisance. So much so, that I have more than once thought about undoing those same four bolts to remove the guard. Your plight has dispelled any notion I have about ever removing that guard.
I've not chimed previously as I have no direct experience with disassembly/reassembly. However, I'd heard that my importer had to removed/replace a PTO shaft that got sheared off while one of his tractors was still under warranty, he may be able/willing to help you out.
Jim Shillington http://www.atlanticimports.ca/home.htm
Ray Hillman at http://www.devonntractors.ca/Index.htm is a Dong Feng dealer and really good mechanic, he may be willing to help you out as well.
I hope this helps.