I could not view your pictures Mike (not your fault -Imgur has stopped working in the UK) so in frustration I ent to Google to find the Holt’s illustrations.
I take it it was Lot 730 in their March 2024 Sale. Very nice rifle but the protrusion of the fences beyond the breech ends does look unusual.
Assuming the C&H did not just do it to look different (not impossible with that firm - they had odd ideas at times) the rifle may have been supplied with a set of 20 (?) bore shotgun tubes to make an all round gun.
I take it that the barrels (if numbered) match the action number?