Nick - I'd be interested in more detail about you saying they broke. That does not tell the story.
Did they break at the welds or at the mounting holes ?
Do you know how to properly weld ?
Did you temper the tines after welding ?
Did you grind the welds after welding and thus creating blue / black hot spots in the grind ?
Do you think the boulder would have broke brand new tines ?
Couldn't you stop before you broke 14 tines , I think a couple would have been enough
Do you think that you should not have been trying to till the boulders in the first place ?
A bounce back hook up on the lift would save a lot of head aches from broken parts.
I hit one rock tilling at night once with my extended width home made rear tine tiller once with my home made tractor and I broke off one whole side from the gear box.
A chain as a top link would maybe have saved it ... putting the heavier 8hp on it in place of the 5hp made it worse too but that's the way I roll ... MORE POWER !