Turns out Merry Tiller is still around, making tillers for rental fleets: http://merrytillers.com/ Maybe you could contact them and get an endorsement deal!

This is a great story because you're at least the third owner, and you got it from your Dad, who welded on it to make improvements, and now you're welding on it to make improvements.

When I saw your before and after pictures the other day, I was wondering: another option might have been to remove the tapered end of the tine and weld a replacement end on... did you square off the taper with multiple TIG beads for any reason? "Because I could" and "Because it's fun" are both fine answers, and I'm not saying either is better or wrong or right, just curious.