Along with lockplate profile one needs consider the thickness of the lock.
I used to have a Pedersoli .45 cal Frontier, Deluxe version. A standard Siler lock would have been a drop-in, pretty much, with respect to plate outline. But the Pedersoli lock is so much thinner that one would have to grind off some from the Siler pan cover & I suppose mainspring to get it to fit.
Likewise I bought a supposed drop-in for the Pedersoli NW gun. American lock mainspring was huge in comparison with the Italian one, would have required a lot of work to make the thing fit. Plate outline of the American lock was OK, just not the thickness.