[FlatheadTed]

Going by past discussions on this subject some states allow 12"x90 .This is not a 35 but is a shot of a 34 spindle its a common fix to add a piece of metal on ether side of the of the 34 spindle when fitting the later 39 to 48 backing plates, this is because of the larger holes in the later ones .We changed one spindle for the sake of Govt compliance requirements so we followed along with what was done previously .I would suggest your chatter problem is because the holes in the backing plate are not concentric to the hub .Also people think a change to juice brakes will give them instant good brakes ,not so it depends on a few things one being the type of linings .Also a good thing to add is a remote vacuum booster hidden some were specially if the car is to be driven a lot at high speed . Ted