I'm in the process of making GP11 drawings, and along the way I've had to confirm the dimensions you're looking for. The GP9 cab is 10' wide, 6' 6" long and 9' 5 1/2" above the walkway at the top of the roof, while both hoods are 8' 10" above the walkway. The pilot-to-pilot distance is 52'. These are per railroad drawings.
From measurements I've taken (from photos, drawings and an actual GP9RM) the hood ends are about 26 1/4" from the pilot face (I've measured between 26" and 26 1/2" depending on the source) and the short hood is 8' 4" long. I haven't measured the long hood, but subtracting the short hood and cab length gives a long hood length of about 32' 9 1/2", and a total nose-to-nose length of 47' 7 1/2" (give or take 1/2").
Edit: I guess you were looking for model dimensions, not the prototype - which I don't have... In any case, at least you'll know whether a given shell is accurate!