Mike
There is a big difference between what a shotgun is for and what a double rifle is for.

Also you would be trying to make a silk purse out of a sows ear.

If you have a 375 SXS double comming you will not want an O/U in 470.

I recommend you just ues your 375 for everything [I have killed buff and elephant with a double 9,3x74R,] or buy a 470 and sell it when you get back, if you find you have no further use for it..

What ever you do forget about that cobbled together O/U 470.