Would be interested to see the stones, if you can post pictures of them... Most mill stones have grooves cut in them from the center out, where the grain is caught and milled. If the ones you plan to use don't have these in them, it could be a lot of work to get them in there. You'll need to decide if it's more work than it's worth. Plus, I see it as taking a long time to mill enough grain for even a single 5 gallon batch (probably even a 2.5 gallon batch). Personally, I'd rather not spend an hour milling grain, cranking a handle, not being 100% sure that the crush is good.
Even though similar methods have been used throughout history, the mills were much larger. Plus they were powered either by animals (mules, etc., sometimes humans I'm sure), wind, or water. Even then, who knows how long it actually took to mill the grain for a batch.
Not saying to not make this, but I would be prepared for it to not do a good job, or take so long to go through enough grain for a batch that you abandon it. Especially when you can mill ~6# in a minute with roller mills.