Welcome to the group! Like Scotty says Hoye is the first place to look and Winston (I think it was him) at one time knew where some pdf files of old Yanmar parts manuals etc were on the internet was in I believe Austrailia (if I remember right) maybe yours was on there?
There is another guy around here that actually has an LS tractor and posts over here some but he also has a 4220D in his sig line check him out he may even have some ideas? That is a big Yanmar the 50hp class they are out there but pretty scarce ought to be a great machine for you imo. :thumbsup: (Gary Fowler is his name I just saw it at the bottom of this page )