Well, 92nd would be easiest, since it just needs a slightly different kilt, and it has no sporran. The hats are arguable similar enough to the 93rd. Here's the Mont-Saint-Jean made for/by the old 75th, you could probably just edit the kilts onto my 93rd one, and then just make the yellow a little bit duller/darker/less vibrant.
However, it should be noted that NCO's would have the custom sporran, but I'll see what I can do about making it, and you can just add it on.
91st would be somewhat easy, since they're very similar to the ones I did for the 93rd (in the picture below, which is well after NW), but the sporran requires some custom work. Maybe I can work something out with that, though.
79th will require the most work, I think. Custom kilt (I'll search for some patterns, but I think it might need to be done
somewhat from scratch), custom hat (similar to the 42nd hat in some respects), and it has yet another custom sporran for NCO. Good resource on 79th: