7.25", 7.75",10.5" from left to right.
I'm sorry. I talking about the actual scarifier shanks. The indentations on the front part of the shanks. Do the shanks only get held by indentation on the top side of the frame of the box blade (where the rod and steel shim hold it tight. If that's so, then the scarifier is leaning slightly backwards as it goes thru the square tub, resting on the backside of the tube as it exits it towards the ground.
The measurements I gave you were from an ebay seller. It was the distance between each indentation on the front part of the scarifier. If it only uses one (the one resting against the top of the square tube, the the spacing doesn't matter. But if it had to be held in two spots the the spacing would have to match up with the thickness of the scarifier tube. Sorry to be a pain in the butt!
I got 2 slots, they made not be the originals scarifiers, measured 1 5/8" between upper n lower, check this link.
Here is a picture of the shanks with the dimensions.