I picked this up last Friday, and just finished putting it back together after cleaning up the wood and refinishing it (in a small way) with boiled linseed oil.
It's a No4 Mk1 from Maltby, made in 1943, and once I got it cleaned up I was pleasantly surprised to find that the bore's really shiny and the rifling looks good and sharp. Maybe I got one that had been carried much and shot little.
I'm not going to clean up the metal for the same reason that I didn't steam the dents and gouges out of the stock. I like that it's got a little character, and it's a shooter. Not a safe queen.
I know they stopped doing unit buttons on these a long time before mine was even produced, but I'd be really interested if anybody's got information on how I can find out what unit it was issued to.