One of those that predates the "T" and "TR" markings.
Any Enfield examiner's marks or "S" on the cutoff block?
Noteworthy that those early rifles were not refinished after conversion, the pads being just chemical(?) blued.
My theory is these early uncompleted rifles, if this is one of them, had their pads fitted at RSAF Enfield after the trials rifles were done and when the foundry supplying brackets was bombed out and the supply dried up until the next foundry/foundries got into production, these rifles were probably put into store to get them out of the way. Once H&H was set up in production and the supply of TR rifles directed to them, I'm guessing those early leftover rifles were forgotten and just sat in store until the post-war clearances began.
Whatever the details of that, and they may well be different , I suggest an interruption in the supply of brackets and therefore in the whole conversion process is the most plausible explanation for these half-converted orphans. RSAF Enfield would have had lots of other work going on and probably no space for things that weren't being used. It might be that fitting of pads continued for some period of time before a decision was made to stop, and if so that would explain the fair number of these rifles that seem to have survived.
Such an interruption in production would also help to explain the very low numbers of No4(T)s on hand in that inventory taken in late 1943 which I've quoted before.