Alf J Parker Twin Zero 4/80 sight

I have just acquired a No4 Mk2 rifle fitted with a Alf J Parker 4/80 twin zero, whilst I have seen lots of the 5c & 4/47 sights this is a new one to me and to date I can't find out very much about its history.
It was fitted to a "Fultons" built rifle, and by that I mean the rifle has been put together from parts, the action has never had a serial number but it does carry the sold out of service mark plus an A over 1099 on the left hand butt socket, the barrel is also unmarked.
I have been told that it was purchased from Fultons in 1984 and has been with the same owner ever since. Interestingly the magazine is marked A.43 so possibly from a trials rifle?

The AJ Parker identification system for their TZ sight was made up of the rifle model followed by the year of design.

The 4/47 (No 4 rifle sight designed in 1947) was replaced by a later model 4/80 (for the No4 rifle designed in 1980)

Another example : The TZ 14/35 (for the P14 designed in 1935) was replaced by the TZ 3/57 (for the No3 rifle and designed in 1957)