modification to the engine block on the #46 tractor.
the bottom model is in the unlabeled blue boxes from the early eighties. some of the twin packs were broken up and issued in plain blue window boxes. i have a few other boxes too
http://img128.imageshack.us/img128/487/fordtractor46sfengineaim0.jpg
http://img259.imageshack.us/img259/2007/blueboxesnoamm2.jpg

That horsebox is the oldest lesney tool that is still being used in China - incredible how this one has stayed in the range......