in between sizes!

I got this pattern and was so excited because I could continue to make shirts for ds who has outgrown the Sketchbook. As luck would have it, his measurements fall in between those for sz 12 of the Sketchbook (and presumably the Button-up button-down) and the XS of the Allday, with the added complication of a neck larger than the XS Allday. Can I take 3/4 inch off each side of the yoke and front without having to redraft the sleeve cap? And if I am shortening about 3-4 inches, should I take some of that from the armscye? I was about to throw in the towel and just make him the XS with a S neckline/collar and have it bunch up somewhat under his blazer... but happened to look into Kamakura Shirts, whose custom shirts start at $130 for a plain blue or white one. Challenge accepted!!.. i think? with your help?