In this case I have to admit I must have been ill informed. It's just, most of the StuGs I've seen had this "Early" or "May 43" muzzle break type (names according to your diagram). Still, not to be picky, but the presented L/48 muzzle break doesn't look satisfactory in my opinion. I can see it resembles the Late type (vide your diagram), but these protrunding sections, look bulgy, instead of sharp.
And on the 105mm topic, I admit I didn't know the "leFH 18M" type appeared on the StuH, but still to me the most 'typical' was the large one, described by you as the "Mid production". Wouldn't it be a good idea to go with the most standard muzzle break type, instead of a rare one, that from what I understand, appeared on a handful of, if not less, StuHs?
In summary, the presented Late 75mm muzzle break looks too bulgy in my opinion, but as longs (as you say you will) as you include other 75mm types (preferably the "Early" or "May 43"), I'll be perfectly happy. Also, the decision on 105mm muzzle break type is quite surprising (I'm talking about the particular shape you decided to go with), but as you said, we can just cut it off, and make a muzzle break-less variant, so it's all good in that case.
