Welcome to the world of LE's.
The main thing to remember is that these were the last of the Victorian era 'hand built' rifles. Do not expect parts from one rifle to fit another (particularly the woodwork) without 'work' being needed.
If you are changing the barrel, then you will need new bolt components to get the correct headspace.
Very few parts will actually 'plug & play'.
Posting pictures of any and all markings will allow you to get as much information from the experts as you can handle.