I can't give you a positive ID on it, what I can say is that it looks like it's been put together from parts, or possibly repaired by someone who really didn't know what they were doing. You can plainly see where the original in-letting for the lock has been filled, and the lock plate looks like a piece of sheet metal (is it NAILED on?) The lock looks like it may be Spanish to me, but I can't be certain. Also I can't really see the side plate on the other side, a clear pic of that might help.
Having said that, an engraved barrel like that is pretty odd, and could be an indication that it was a very high end musket in it's time, possibly a presentation gun. You'd need to get it looked at by an expert though to confirm that.
Can you post clear pics of the left side plate, a straight on close up of the lock, the barrel engraving, and any proof marks no matter how small they are? I'll help you as best I can to ID it, but I simply cant from the pics so far.