I would suspect that the Colonial VA, Early Ketland size locks will be larger than the Siler mortise. You would have to open up the Siler mortise to fit the larger lock but those locks are pretty much the standard for a fowler.
You can go to one of the online supply houses such as Track Of the Wolf and see the dimensions of those locks to make sure they are large enough to cover the Siler mortise. The TOW catalog has full size photos of these locks.
Dennis