yes 28-29 coupe fixed seat are the same I have one I put together for a early 68B that I made for an ajustable seat. I also have a couple 28-29 package trays. if you needone let me know.
I think there may be a couple variants to the 68A package tray. Mine is for August 1929 car and is the same as I have seen on a couple 68B's on Bob Johnson's cabriolet site photos.
Mine bolts below the belt rail while some may have steel straps going higher and nailing to the belt rail wood rather than using bolts through the belt rail.
My 45A coupe, as I recall has sheet metal strapping flanges from the tray's base to the wood above the belt line (all one stamping, I think). I do not think I have any photos of it; but I recall seeing a cabriolet photo or two showing that type of mounting of the package tray.