When talking Darne guns, 24 was rare in Europe, too. I asked Hervé Bruchet, 20 years ago, if they still built 24 gauge guns, and he answered, "Yea, but, I don't know why. Nobody buys them. I don't know why they would".
And so it goes. You have not lucked into a winning lottery ticket, just the lowest grade Darne R model gun, with brazed barrels instead of monoblock barrels, in a gauge that is hard to feed. Not impossible, mind you, but, you will have to really want to shoot it, in order to do so. Most of the 24 gauge Darnes I have seen were 2 1/2" chamber guns, as well. The barrel flats will be marked 6.5 or 65 if that is the case.
There was, at one time, a specific "Halifax" buttplate. Older guns often had horn that had lines cut in it (my Halifax is so equipped). The Dutchman buttplate is a reproduction of the typical R model buttplate, and would be perfectly usable, in addition to being made of stable ureathane, instead of the organic horsey hoof plastic the original was, which, is not stable, and tends to shrink and/or crack.
The screws would have been lightly engraved, with a thin slot (NOT phillips head) and skillfully aligned up and down.
Pictures would be good, especially a clear one of the flats of the barrels. You can email them to me, and I will post them here for all to enjoy or to be scornful of.
I like to think that the scornful wouldn't know what to do with a tray of broiled butter and garlic escargots, fresh off the grille, while Brigitte Bardot was sitting next to them, with a big jug of Fischer Alsace in her hand.