As stated above get 26 inch barrels. Don't go and buy a custom made double rifle with 24" barrels when you can have 26" barrels.
I would not buy a 375 Flanged double. Brass is too hard to find. 9.3X74R is a better choice in my opine.
Or you could just go ahead and get a 450/400 3 inch.
Hornady is making brass bullets and ammo for both.