The following is NOT a substitute for an appraisal, but it'll be a start, and offer a "rough guess" as to age/value.
First thing, swords worn during WW2 generally had a "retaining pin" that held it firmly in the scabbard. You'd hit a button to release. Normally that's a bad sign, but sometimes a GREAT piece of old steel will be lurking in such a "modern type" sheath/grip combination.
An old blade may have a distinctive feature: good Japanese swords will NOT have "flat sides", they'll come up from the cutting edge to the fattest point, they'll then get slightly narrower towards the spine and then they'll have a "blunt ridge" at the very spine. But the GOOD old stuff will have a "battle bulge" at the tip, where the upper side faces "flare out" and then come back to the tip. This "bulge" reinforced the tip and made for a fat entry wound in front of a slightly "skinnier" blade, possibly having a "blood groove like" effect. That's one theory, anyways.
To do a proper appraisal you'll have to seperate grip from blade anyways. Stick the tang on a scanner and record the maker's marks on one side, save as .JPG or whatever, stick it on the web and put a pointer to it over at www.swordforums.com.
Also: take a close look at the mount hole in the tang..."the real thing" will have been punched out with the metal hot and this will be obvious versus something done with a drill press in the 20th century.
Fullers (proper term for "blood groove" which was probably no such thing) aren't too common on Japanese pieces. Not unheard of, mind you...double-edge swords/knives are also seen sometimes.
I'm a beginner at all this myself, so if I'm wrong on any point please correct me.