Might have been '81, thought the inside of my old KT had '74 stamped in it. Have to look.

Lower hull. The older one did not have sponsons to cover the tracks, and the rear hull mount was a thin metal side to side bracket. Also if memory serves the transmission mount holes were different, and no machinery deck or holes therefore.

FO hull has bolt on aluminium sponsons almost full length, upper hull mount is normally the speaker, an electrical equipment deck is included, and the holes for TU are correct for the dual trans systems.