Jumping into this discussion rather late so excuse me if I missed something above.
The English locks found on the handful of Scottish long guns are clearly replacements. Over their working lives -and their lives as collectibles as well- many of these guns went through repairs, using older or newer parts with mixed dates, and modifications such as the aforementioned locks, triggers and trigger guards to "update" them. When Whitelaw and Blair began to write about these guns their then owners sometimes "backdated" them to their previously documented condition. An especially ornate piece by William Smith is a prime example. It originally had no trigger guard, then it did, then it didn't, if you get my meaning. There is no indication that any of these guns, with the exception of the 18th c. Gwynn piece, had anything but the Scottish - made snaphaunce lock which which we are familiar.
This complicates things a bit in that TRS does not supply a Scottish snaphaunce lock and the English style simply isn't really appropriate, unless you build a long gun which is supposed to have had its lock replaced at some point.
I agree that all of the extant Scottish national longarms were originally snaphaunce weapons, and the two that are not were converted. I am not against having it made to be a snaphaunce, however the issue is it is just as you said there is not a readily available Scottish lock. I am currently trying to figure out if a firearm which has been converted to a more recent lock would be more appropriate for the beginning of the 1745 uprising that a snaphaunce?