hi AHS,
very common problem with the 300, 400 and some 500 series wh tractors. i used to use 1/8 X 1.5" angle iron like ri702bill suggested. now i buy a kit from brockport bill. bolts right on. easy- peasy. also ri702bill makes a nice kit to reinforce the 'F' plate. both kits are well worth the $$$ imo.