My thoughts... The comb appears to be worn down some ahead of the buttplate tang. Not a tremendous amount, but some. Just extend the line on top of the buttplate tang forward to see where it likely originally was. The buttplate, I don't know... The positions of the nails looks odd to me. I'm inclined to think, though, that it is the original buttplate. I think it was made box-less, and the sliding wood patchbox is a later addition. The lid that's in it, doesn't even have a catch! I don't see why the triggerguard would not be original to the gun. I would not discount the full-panel sideplate as original either.