Sorry for late reply Ferrylaki but seems my e-mail doesn't receive
addvise of new posting in subscibed threads. I've to check my profile.
Now chances you've an antique one remounted for WWII purpose are
increased. Likely the assumption "re-mounted, in oblivion and then badly
polished" is the right one. Don't sell the saya (obvious enough..).
Don't make anything more on your own to the blade and tang other then oiling/cleaning it with paper unshented tissues.
Remove the Habaki (collar), keep the blade lightly oiled and OUT of that saya because likely it retain moisture. Mineral oil, not engine one.
Simply wrap the oiled blade in newspapers.
Your climate should be very humid. think about this when you choose the place where to store the blade waiting to find someone knowledgeable enough
to make an "on-hand" appraisal. NihonTo Message Board surely can address
you to someone to have a window polished to have a better
understanding of the period and to evaluate an eventual restoration.
Remember that such restoration will mean a complete polishing, a new plain wood scabbard and handle (shirasaya) and most likely a new Habaki (collar) too. Not a cheap trip, and possibly not economically convenient.
Depends on what sort out from that "window".
Be aware. NihonTo are like vampires. Once you've been beaten you are doomed...