In the photo it looks like your trigger guard is iron. Unless I'm mistaken, I don't think that there is any model Brown Bess with iron furniture, at least the Brown Bess's I have knowledge of all had brass furniture. Just because your trigger guard has an acorn finial doesn't make it Brown Bess, lots of other guns have acorn finial's on trigger guards. Nothing about your musket says Brown Bess to me. Your musket might well be a parts gun, but the parts certainly don't appear to be from a Bess. If the trigger guard on yours is brass, then you have a slim case.
This is a third model Brown Bess lock. Note the difference. See how rounded the lock plate and hammer are.
This photo is a close up showing the markings on the lock, and all B. B's have those marks, and the next picture shows the standard brass side plate used on all models of Brown Bess.
And finally, this is a brass trigger guard on a 3rd model Bess.
There are lots of other identifying features of a Brown Bess, but you would have to show the entire gun for those to be seen. Even though made in India, before interchangeable parts, these guns were still pretty standard. Take a flat piece of brass, put some oil on the lock and use the brass to scrape the excess rust off the lock plate so you can see the markings. That won't ruin the value of the gun at all, anything else will. Most anything you do to the gun will cause the value to go down. Wash it with soap and water, oil it, use a good quality, NON PLASTIC base oil on the wood, like linseed or tung oil, NOT varathane or spar varnish. Use light machine oil on the metal. NO WIRE BRUSH, remove rust with oil and a brass scraper. If there is an elephant stamped on the lock plate, you will make me eat my words, but right now I can't see Brown Bess on anything you are showing.
The photo is a Brown Bess lock, note the markings on the lock, and the shape of the hammer, it's a goose neck. The Brown Bess also had all brass furniture, nose cap, trigger guard, ramrod entry pipe, ramrod pipes, butt plate, and the side plate opposite the lock. Your lock looks to me like it might be Harpers Ferry or Springfield. I don't remember well enough anymore to pin that down without lots of research.
This is the Harpers Ferry musket model of 1816, and the next one is the Springfield musket model of 1795. 
Both of these guns had all iron furniture, but the markings on your lock and these don't match up.
Here's a picture of a Harpers Ferry model 1803 rifle and a picture of lrgcent's lock, and lrgcent's lock matches the rifle lock way better than any Brown Bess.
