Gents:

Our gunsmith built himself a 450 No 2 on a French 16 guage frame (sorry - don't remember shotgun maker) and it came out rather nicely. Up until then, did not know it could be done.

What would be a recommendation for a 450/400 to be built on a shotgun frame?

I have built quite a few of these conversions using shotgun and rifle actions. I prefer converting heavy shotguns with thick "walls" long action bars and Greener crossbolts, or dolls head at least. Traditional waterfowling shotguns are a good source of actions.

Could you offer a few specifics please?