You could remove the brkt from the frame, install a standard poly bush and brkt on the bar, then build an adapter brkt to go between.
Another option is you could bend two 1/2 inch wide and one one inch wide by 1/8 strips, lap the center strip over the sides slightly and weld them together (looks like a top hat from the end), then weld to the brkt. About $10 worth of steel from the home improvement store.