is it practical
Completely impratical.
The barbette for a twin 409mm turret has a larger diameter than that of Fuso's 356mm ones. That would require the barbettes for turrets 1,2 and 3 to be removed and the internal structure gutted to get the extra space needed to fit the new barbettes.
The funnel sits above the former N°4 barbette, which implies boiler room spaces has ben modified and somewhat moved aft by replacing the aforementioned barbette (more gutting of the internal structure).
Last but not least both N° 5 and 6 turrets and barbettes would have been removed to be replaced by a single turret sitting inbetween. this not only requires even larger modifications and internal gutting of 1,2 and 3 but for some reasons the new turret is a triple, which means an even larger barbette is needed. Japan also did not manufacture any triple 409mm turrets, which means that, at best, just four wold be procured (if we stretch out things and assume Fuso, Yamashiro, Ise and Hyuga somehow all getting this treatment). This notwithstanding fitting the much wider 409mm barbette is even possible aft, for example Ise and Hyuga, which were very much Fuso half-sisters had very cramped afts.
Removing the original forward tripod for a Nagato-esque heptapodal (7-legged) mast seems also needlessly complex.
The only thing that is perfectly fine to me is the aft superstructure (too bad the funnel placed so aft makes very cumbersome to use the boat boom).