Hi Richard,
Another neat project I see.
Although Mark is right about possible cost savings, there's no substitution for getting the self satisfaction of making your own box. Plus it's a little harder to re-design an existing boxblade to get the hydraulic lifting feature for the scarifiers you want...but it can be done.
A couple of things I would consider with your design, and this is only a suggestion, not a critique mind you.
Since you know that a boxblade's performance is all about weight, I would thicken up every single component. Not just for the added strength and resistance to abuse, but for the added weight. That will make your boxblade perform better in every way of use...from ripping to digging and smoothing etc. So I would consider going from 1/4" thick plates to at least 3/8" if not thicker. And so on for the other thickness plates and bars. Even your 3pt attachment. (Just my 2 cents)
Another thing to consider is what kind of scarifiers you will use. Some have the holes in them for positioning and others have slots cut out. I've found the ones sold at Agri-Supply are inexpensive and very durable. I got the ones with the holes in them because I bent and broke the ones with slots right at the slots. It is a natural weak point in the shank, whereas the holes are not as much.
If possible, could you show a section view from the side? Like if you were to remove the Left or Right side plate. I'd like to see how you are going to make the scarifiers work with the pivot and hydraulics.
Thanks,
