Having now found oshigata it's not a match as the Joji morihisa signs: 備州長船住守久 Whereas mine is 備州長船住盛久.
The only other Morihisa that comes close is from Markus' Index :
However, mine is dated 1375 which is when Moromitsu started working and from the dates would most likely be too early for a younger brother unless "tradition" is wrong. It makes no sense for it to be gimei as there's at least 20 better smiths working in Bizen at that time Like Masamitsu, Morikage that would be a better target and I doubt the Joji Morihisa changed that kanji (the rest of the signature is distinctly different as well). It's Suguha with Ashi and is distinctly Oei or earlier Bizen work so not exactly a late muromachi copy. It looks like it'll be very nice in polish with a very bright, even hamon, good nioiguchi etc Without the mei I'd haf expect it to paper to a better smith.
So I am thoroughly confused, anyone have any theories?