Sea Chest Half Mortise Lock-Need help identifying

[JLDavisSeaChest]

I inherited a sea chest from my great grandfather who lived in Philadelphia, Pennsylvania, US. I know the sea chest dates from at least 1849 by corroborative provenance, but I am trying to determine how much earlier it may have been made. I have been informed that the lock, which is identical to the photo, is English. My lock appears identical in every respect except that the lock says 4 TUMBLER in the curvilinear stamped area. Would any one have any idea who produced these locks and/or when they were produced. It is possible, I suppose, that the lock was added after the sea chest was crafted. Thanks for any possible help.