Bar-action hammergun here. Easy to make a pistol-grip stock curving downwards behind the trigger-guard.

Back-action hammergun here. Virtually impossible to make a properly proportioned pistol grip behind those locks, and still reach the triggers with your finger!

So while a vintage original probably has to be back-actioned (with curved lock-plates) to look the part, a modern conversion of a hammer shotgun pretty-much cannot be back-actioned.

And I agree with other posters here that the saw-grip needed to prevent a top-lever from busting the web of your hand is ugly as a hat-full of Rsoles!