Custom made rolling block pistol, disassembled, with british proof marks.  Likely from 1890-1920 time period, think this when most of the custom pistols were produced by individual gunsmiths.  I don't think it's a factory original, but instead is a rework of a factory one

The Proof Mark shown on the barrel is Belgian, not English. The receiver is similar in shape to a Remington No.4 and may be Rem, but the extractor and shape of the breech block don’t look Remington … I may be wrong. This may be a Belgian copy in pieces.

See if you can locate a copy of Remington Rolling Block Pistols by Landskron. Chapter 24 covers foreign rolling block pistols -&- Chapter. 25 covers pistols on Remington Rifle actions.

The best advice I got from a friend that helped me a lot … buy one to two books for every gun you buy. A reference library is very helpful.

… Joe D

Yuank you. I knew it wasn't Remington but had no idea what the proof marks meant.

this is a  fully Belgian made rolling block, and not a modified n°4 Remington.

They also made boys rifles on the same receiver.
I have given one to my nephew and have another one in the workshop awaiting much needed restauration.