Designated or "undesignated" action? Depends on the length of the barrel and the OAL of the rig. Consider a left or right hand rifle action set up in a rear grip stock. Shorter barrel (as long as it's at least 16") could probably get the same style you after? And less work than messing with the trigger on a Striker.
Left hand model 12 makes a real nice Striker type SP. And deadly accurate to boot!
Or, if $$ isn't a problem, go with a target action. I prefer a rifle action so I can shoot it both ways (rifle or rear grip SP). And a rifle action with a small shank barrel has more options for parts swaping.
If you're a right handed shooter, the left hand rifle action works like a dream.
Keep your right hand on the grip and work the bolt with your "free" left hand.
If you're a lefty, go right hand action and use your right hand to feed ammo and work the bolt while your left hand holds the grip.
Takes a few minutes to figure out why you didn't go that way a long time before.
As far as the Specialty Pistol forum? If you hang around there too long, the $$ will fly away from your wallet and you'll be wondering why! Too many good ideas to pass up.