I'd say it's way too much trouble, thus expense, for what you end up with.
I might be wrong but I don't see it as being much more trouble than a rebarrel. The bolt face would need work and might have to work the rails?
I shoot a 300 Rum barrel on a 338 Win Mag (I believe all the Rem 700 Long actions are the same length for the Magnums).
No offense, but I don't like Rem actions, mostly because of their style safety. Otherwise, I would just use a 700 RUM action and this wouldn't even be a question.
However it is a single shot configuration. Plate glued in and an ADL type stock.
I definitely want the use of my magazine. This will be an all range rifle, short and long and will be using it on bear also.
If I had a 300 Win Mag I'd stick with it rather than consider using a reduced case capacity.
There won't be any reduced case capacity in this configuration other than a deeper seated bullet which will not affect capacity for powder as in requiring a compressed load.
What would be super, I think, would be to chamber for a 300 Win Mag necked up to 338 which may be a more straight forward way of gettin' 'er done.