fordman, nice project you got going.
Looks like you got a real nice workshop with a lot of good tools to do about anything you want. The boxblade looks like it will be pretty heavy and it's interesting that you're using that I beam instead of a square tube for the scarifiers.
I think it's great anytime I see someone get with it and do a homemade project like that.
If you are up for a couple of suggestions, I would consider what Renze said about adding a bar or gusset where the scarifiers are located on that I beam. If you plan to do a lot of ripping the I beam may tweak right where the scarifier is. Especially if you DON"T plan on doing a lot. That's always when if happens.

It's not that much more work and good insurance.
The other suggestion I have is again, if you plan to use those scarifiers a lot, you will find it pretty aggravating after a while getting off and on the tractor to adjust them. You have the perfect opportunity to make them adjustable up and down right now. I can see you definitely have the talent, so that is no question.
Using your design, I would consider a gantry type system with linkage and a lever attached to a shaft that you rotate. There would be an "arm" or a couple of them welded or fastened to the rotating shaft and the end of it pinned to the scarifier bar to lift or lower the scarifiers as the lever rotates the shaft. Connect all the scarifiers to a bar that spans them all. The scarifier holder bar is moved up and down by the system and the scarifiers move up and down. The link is from the end of the shaft "arm" to the holder bar so they can slide straight up and down as the bar is rotated. Correct geometry will keep the bar moving in one path rather than being pulled off to the side when you rotate the lever.
You wouldn't need the individual scarifier positioning pins then, meaning you don't have the take them all out to move the scarifiers and put them all back in. Rather make a plate with holes in it next to the lever. Pin the lever to the holes in the plate for various depths/height. You could make it manual, meaning you need to get off the tractor to raise or lower the scarifiers, but only have to deal with un-pinning the lever and re-pinning it. Or, you could add a hydraulic cylinder that moves the lever. You could run it from your rear remotes.
Just something to think about. (lol ... like you needed more project time

)
The upside to any of that is you will be adding even more weight to your beautiful blade.
Rob-