Your poor rifle has had the woodwork thrashed with a sander to within an inch of its poor life and is beyond any sort of help by a total amateur with a belt sander. That's only my opinion Jeff as one who had fixed and range tested a few - thousand!
Just a small point, the Technical instructions and Amended parts list shows that from the early 50's, ALL No4 similar parts supposedly 'special*' to the No5 rifle, such as the sear, bolt, backsight screw and nut - and probably a few other odds and sods - were obsolescent. And annoted alongsine is 'WSE, see OPL5593'. In short, this is the standard No4 parts list. Thereafter the No4 parts became the norm/standard. However, it was clear that what'd really happened was that parts supply had been standardised.
So in the real world of an Armourers shop - as opposed to the fairy-tale world of collectors and concours fiends, in the main workshops a standar No4 bolt or, say, sear would be used in the normal way.
Just as a matter of interest, if your No5 has a thin steel plate between the butt pad and the butt, then get rid of it if it hasn't already rusted out/ These steel plates were a pain in the ar....., bottom, as being totally enclosed, they'd start to rust out and the wet steel corrosion would run downwards into the butt plate cup and destroy the long two-part retaining screw/nut OR if the rifles were kept muzzle down - as many were. just run into the stock bolt and set about that too. A real menace!
Incidentally, anyone out there got butt plate cup(s) with small 'U' shaped recesses cut into the top, bottom, l and r sides around the bottom edges? That was one of our modifications to let the festering water out of the butt. How did the water get in trhere? It's called the monsoon. Lasted from the beginning of September until midway through the following August. Or so it seemed!
Nice rifles but really not as manageable and tough as No4's
* some of these so called 'special' parts weren't really special at all but just natural progression - like waisted trigger guards that became the norm eventually