No, the 3 hole mounting area became standard a few years after the original production, and all calibers can have them (at least according to a few multi-Mateba owners). Plenty of .357 versions with the 3 holes on Google images. Don't know if the option was there after to have it not included, or if the option was even available to be included on the earlier models. Also don't have a clue as to which way they're making these current versions, but if the IWA 2018 photos are accurate, they should have the 3 holes.
Edit: could be an option on the .357's later on. They definitely made them, but the # of them I'm seeing don't seem to indicate they were standard as some people I talked with said they were.
As for barrel length & shroud options, we really, really, REALLY need a photo of what we might be purchasing. The shrouds change depending upon the threading option available, as an 8" can either be flush with the 4-ribbed shroud if not threaded, or extend past the 3-ribbed shroud if threaded. Same principal applies for the 6". As for the 5", could go a few different ways as well. Once again, the pics at IWA 2018 show threaded & compensated versions - but is this what we're supposedly getting or not?
Edit 2: also wondering what sights there are coming with? Seen straight black sights, sights with dots (which they currently have listed under parts), and actual fiber optics of some sort.. though for these I'm unsure if factory or not?