I'm not home yet, but from what I understand about what Rootes was doing for
the Alpine GT versus the Sports Tourer for Series III and IV is that they
wanted the GT's to run quieter than the Sport Tourers. The bonnet padding is
one change, and I believe I read that the air filter housings for GT were
different as well, which may account for IIRC lower horsepower ratings for the
GT versus the Sports Tourer. I don't remember if Rootes did this for the 1725cc
motor, I'm a little more certain that this applied to the 1600cc cars.