Looks like a Woodpecker to me. All my trees are like that. And the racket they make when they try on the aluminum siding of the house or on a street light.
I believe that they were thicker and heavier than the OEM blades and they installed with the standard hardware with no problems. I got them from yardparts.com but they don't seem to carry that model any longer.
I bought these for my 48 inch MMM. They are very thick and heavy. Cheaper too. They seem to cut marginally better with less vibration and the edge seems to last longer.
I have upgraded my BX1880 with the larger tires and the 48 inch narrower mower, which brings the rear anti scalp rollers closer to the tires than the 54 inch mower. I have no problems. Something, does not seem right.