"I tenatively plan on hunting my Merkel then selling it and upgrading to a more versatile "fun" qd scoped 450/400 and scoped 9.3 x 74R Double(Is a 9.3 x 74R extra barrel possible??)" The answer is yes since I have seen that done, but perhaps you may not want to do so for the following reason.

A 9.3X74R can be built on a smaller 'frame' and is generally lighter built than most 450/400s. One solution would be to buy a Chapuis in one of the lower grades (I think William Larkin Moore has one in the 6,000 range) and they come set up to scope quite easily. I have handled several of the 'low rent' Chapuis doubles in the smaller calibers and 'lesser' grades, and they are very, very nicely finished, not 'cheap' in fit, finish and styling elements, and shoot very accurately.

Why make one double do double duty (sorry about that) when you could get a nicely-maintained or new 450/400 and get a Chapuis for the price of a second barrel set? The latter would be easier to handle and less of a hassle in changing barrels, scopes, etc with the two barrel set up on an inherently heavier gun. Dave