I think you have the basis for a good flail mill there.
I built mine out of a piece of pipe of indeterminate composition, diameter about 13 inches wall thickness 3/8'' ,width 4'' (100mm) The chain I used was a bit of old high tensile lifting chain arranged in a cloverleaf pattern around a 25mm shaft. It is side feed & side discharge as I believe this is a bit easier on the screens. I powered mine with a 6.5 hp chonda knock off with centrifugal clutch. Its cheap but works ok.
It takes 65mm stone and reduces to 3mm & smaller dust in one pass & feeds at about 750g a minute.