Here's another vote for a SxS howdah pistol.
My current "occupational" field carry is a modern .357 stainless revolver: practical, sorta, but too much piss'n'wind in reality, and it has no soul.

My fantasy howdah pistol would be a side-lever hammer (bar-action sidelock) chambered for a 16-bore x 2-inch brass case, loaded with round ball.

...and definitely rifled barrels!

Shhh, don't tell anyone, but I already have a donor shotgun squirreled away for a rainy day. Do you know how rare British bar-action hammer-guns with percussion-style fences really are in Australia? Almost as rare as slow-twist wide-groove/tall-narrow-lands 16-bore tubes!

Alas, many rainy days will likely come and go before this howdah pistol project gets off the ground!