If it is a replacement, it would have been 'sold out of service' and have the two opposing arrows on it -x-, just above the (crown down arrow) acceptance mark. I can't see that. It would be civilian proofed too - no sign either. The examiners marks are all Birmingham. I would need to see more photos to go any further.
*Lock replacement - easy to do. I have a Snider-Enfield Artilery carbine new made with a steel barrrel. These were made in Enfield from 1869 onwards. Nowhere else. The lock has a well-engraved large crown with VR between hammer and nipple. This is NOT the way it was done after 1853. On stripping, the lock has LAC stamped on the inside. They went out of business in 1866! It looks like a relatively modern apprentice piece on a rather rusty old carbine!