Post 1, Photo 3, Receiver ring, Marking "Crown 55 B". The "B" is in Italic type, indicating Birmingham Repair. It is stamped deep and is mushed sideways a bit, but it is still Italic. I think.
The missing Bridge Charger Guide is not a huge problem; they are around. Riveting the thing on is the hard part!
The old Redfield aperture sight is a collectors' piece on its own.
Correct wood for this one would be Walnut, either English or American would do the job.
Lot of SMALL parts need to be found, but they are out there; even I have a FEW. Gun shows are great, junk bins a wonderful source. Trouble is that you have to KNOW what you are looking for; it would be a terrible SIN to try to adapt a MAUSER rear-sight base to an SMLE!!! The parts appear similar if all you have to go by is a picture..... but they are MARKED entirely differently. The British marked all parts VERY thoroughly and their stamps cannot be mistaken for anything else.
While getting together the parts you will need for a restoration (which can be a lengthy process if you don't want to spend a ton of money; it's also more fun) there is no real reason that this should not continue as it has for the last 50 years: as a hunting rifle. It WILL down anything in North America and it WILL keep the Freezer full.
Parts-getting-together time is also well-spent learning about the rifle..... and learning to load your own ammo for it (saves 60 cents on the dollar or more AND gives you more accuracy).
Be sure to re-read Post 3. THAT is the BEST advice I can offer to a New Pal. The rest is just technical!
The SAFETY does have an issue: none of mine do that. They promised that they would not; I promised to feed them better than I eat, myself, and so we have an agreement! Likely wear on the safety CAM. Several reputable places have the parts. Also COULD be faulty Trigger/Sear/Cocking Piece engagement, depending on how much out-of-spec the parts have been allowed to get over the last 96 years. It is a safety issue, but it is repairable relatively inexpensively.
Anyway, hope this helps.