i had searched out a few photos of reliance guns; https://www.gunsinternational.com/g...e-12ga--sxs-shotgun.cfm?gun_id=100967340
https://www.gunsinternational.com/g...4--nitro-proof.cfm?gun_id=102627810#lg-1

and courtesy of larry's tip i did find one example of a continental, from a morphy auction a year ago: https://auctions.morphyauctions.com/lot-593731.aspx
and from france, a much later version, that's evidently greener bolted (?) https://www.naturabuy.fr/fusil-chasse-cal-20-item-9833609.html

but each example i have found has the single curved indent at the rear line of the action body, and has a step down to a pinched section, at the front of the bar, and all of them have conventional english barrel lengths.

and most seem to be marked with legends on the ribs, rather than at tdc on the tubes themselves - just enough differences to be puzzling.

thanks to all for sharing knowledge.

best regards,
tom

"it's a poor sort of memory that only works backwards."
lewis carroll, Alice in Wonderland