As rebuilt the fans are a case of 'anything goes' so it's possible a 48" fan loco could come out of shops with 36" fans, if you get to the point of tracking through the numbers you'll see what I mean. I'm struggling to find too many pictures of NAR GP9s in absolutely original condition, but this page has them in CNR ownership:
4600s - GP9 if you haven't found it already.
Yep, I suspect I'm looking at different engines than you (!!), 7069 was one of my targets. The only GP9 I saw in Canada, at Trois Rivieres in Quebec. The other one I was looking at doing was 4115...
In terms of details you've lit upon a one-off*, in the same way I could say the Kaslo kit is 'correct'; it is for one loco! In terms of doing a loco that's been with CN from new and rebuilt as a GP9rm you've got the whole of the cab and nose area, steps, pilots, anticlimbers, long nose end, brakegear, bodyside louvres (and a couple of doors/latches) and modify the brake blister, fuel tank and that's just the big handful stuff, if you're doing an ex-lightweight unit the frame needs changing too. I reckon I can knock out a couple of rectangles of material for the basic body easier than prepping an existing one and lo - scratchbuilt model.
Steph
*May not actually be a one off, I concede, but there can't more than a handful. As Fraser pointed out earlier, all CN's GP9s were built with an unusual arrangement of grilles to clear the original name 'banner' when in green livery.