Yeah, agree with Curl. The CZ Rigby can certainly jab you if loaded 'without modesty', whereas a .470 has less recoil velocity in a sensible-weight double. What does the Merkel 140 weigh?
If it's 10.5 to 11 lbs, fine. If it's closer to 10 lbs, Hmmmmm....!

Your choice of the .470 has my thumbs-up. Be sure to let us know the outcome!