Well, consider that I know nothing about Long Branch rifles, but the bolt and left side of the receiver buttstock socket (if that's what it's called?) both have the same s/n, which is 4L4093. I don't know what the "LB" stamp should look like or where it should be, but on the front part of the bolt, the part that unscrews where the extractor is, there's a flat area on top with what looks like an L and a B almost on top of each other. The B is sitting on the lower leg of the L, like right "in its lap". That round cocking knob you mentioned also appears to have that same symbol stamped on the lower right side. There also appears to be some other stuff stamped there, but way too small for me to see, although I can make out a very tiny 5 there. The other "stuff" may just be from wear marks too.
What I really need is an "Enfield Expert" to look this rifle and my others over. Does anybody know of any Enfield Experts in the Denver, CO, area?