The Japanese Acoustic Black Widow

The Japanese-made Black Widows were made very similar to their ancestor, the Bartell/Hohner bass. They shared the body style, pickup design, and the 3-bolt neck mount. They were built by Matsumoto Moko or the Hosino factory in Matsumoto, Japan.
Looking at the pics, you can see many differences from the Mosrite versions. Here's a list of things that differ:

Critical differences of the Black Widow versions

Item	Japanese	Mosrite
Neck Mounting	3-bolt with 2 on back, 1 in front of bridge	4-bolt in back
Pickups	Black and chrome with 6 polepieces	Black and chrome with 12 polepieces
Bridge	2 stud mount, similar in appearance to strat bridge	Standard Mosrite adjustable bridge
Binding	Triple-ply on body and headstock, single-ply on back of body, none on neck	Single-ply on neck, body, and headstock
Serial Number	Usually stamped on plate on back, may be on end of fretboard	Imprinted on fretboard below 24th fret
Nut	Zero Fret w/ drilled metal bar for spacing	Zero fret w/ standard Mosrite metal nut

Note that these are not written in stone. There have been instances of mixed features such as a 3-bolt neck and Mosrite nut or imprinted serial numbers on Japanese fretboards. Probably the most definitive way to determine origin is by the neck joint. Japanese and Bartell instruments should all have the 3-bolt neck attachment (2 in back and 1 in front below the bridge pickup). The Mosrite models will have a 4 bolt attachment on the back.