While there may be more minor difference, I think the major ones are:
- On the compass bridge (on conning tower right behind 2nd fwd 16in gun), Mutsu had four portholes, Nagato had two
- On the secondary gun standby control room (same level as porthole differences), Nagato had enclosed windows while Mutsu had simple openings normally covered by canvas
- On forward deck near bow, pair of open chocks were closer to the bow on Mutsu, Nagato chocks were a little further aft.
See Mutsu colorized photo here:
This info is from Imperial Japanese Navy
Battleship Nagato Super Illustration. There are also differences in location of various deck skylights, ventilators, stern recognition lights and the aft mast but these are difficult to describe without graphics and I don't have an image hosting service.
: Dan Kaplan is the IJN expert,he can give us
: some useful info about this matter.
: I have both 1/350 ships from Hasegawa and
: only differ in 1 sprue,have not checked
: properly but looks like the shelter deck is
: a bit different ,and the case of Nagato,got
: lots more A/A guns added afterwards,but You
: can build your model in a Nagato without any
: issue and maybe 1 out of a 100 people will
: notice is the Mutsu,Im pretty sure that both
: Nichimo models were the same as You referred
: earlier with the Doyusha example