Great idea! Might need to measure to make sure there is enough room under the frame and ahead of the blades.
I'm thinking of building an aerator of sorts. My plan was to cut some star shaped disks out of 5/16" plate, weld them to some hubs, put that on a shaft in a frame and hope it would work.
Manufactured aerator spoons cost about $2.50 each and you'd have to have a complex mount to mount them, so that price would add up.
I've thought about finding an old farm type rotorary hoe and using those wheels as diggers. Not sure how well it would work in a lawn.
You are correct in that the box blade has all the structure. I would think that you could buy some bearing carriers that would bolt up to your side plates, then you would have to cut a slot for the axle and bearings to drop out of when you wanted to remove it.
An interesting idea.............. THKS.
Ron