"ZF" marking on Enfields?

[Son]

I have begun the inspection process as best as I am able in the hope to find something to indicate why my rifle is marked ZF. I have decided at this point, from the information in this thread and the posting from Peter on DP rifles that I will not be firing this one anyway, as the probability of it being ok is getting less as I get further into it. Looking at the fact the foreend is numbered to the rifle, and the butt is a good colour and grain match to the foreend, I must assume it is original to the rifle. I managed to track down the previous owner, he had neither altered nor fired it while in his possession. He said it had come from a re-enactor who used it as a rifle scabbard filler, and unlikely he had fired it either.

In service life, everything except the receiver are replaceable parts. The "ZF" must be related to the receiver. Excessive headspace, and therefore worn locking lugs are not the problem. It headspaces as good with it's #1 bolthead. In the next day or two I will examine it very closely under a magnifying glass and good light. Until then, here's a couple of unusual things I found (maybe someone can help me out with the markings?)

There has been a wooden block inset into the foreend under the barrel reinforce. Maybe Peter can confirm it as the type of thing that might be done by an armourer to get the bedding right- maybe it's common- (this is my first No4).
The R side of the receiver is marked C28 under the wood line. There is another mark on the butt socket, L side under the serial. It looks like C (or G) and 30 (could be wrong there too- will double check tomorrow.
Pics below.

Any and all comments welcome.