I received mine from HF less than a week ago. The slots for the lower arms are 1-1/2" wide. The distance between the lower hooks is about 26-1/2", and the distance from outside of one hook to the outside of the other is 29". The sticker says it meets ASAE specs for category 1.
I also bought a cat 1 drawbar to use for modifying a back blade that won't fit the quick hitch, I dropped it into the hooks for a look see. The drawbar is 26" wide, so no problem there. The pins (7/8"?) fit nicely in the bottom hooks, no room for bushings if I'd wanted to. I could use some spacers to take up the slack between the hooks if I wanted, but it's only 1/2", not much movement there.
Monte