Didn't see there was a Longines forum here when I posted this in the open discussion! Hopefully some of you Longines lovers will chime in!! Here was the post:
Picked this up 2 weeks ago for $100. Was unsure for about a day and considered returning it because I seriously thought it was some custom job. I scoured the internet to find just two other examples of the same watch online. Here is one of them My watch is in near perfect condition aside from missing the gold bracelet. Smaller watch at 30mm, but very unique looking. Strangely a great looking watch IMO, Thoughts? Still waiting on a response from Longines with further info regarding this!

 

Serial number puts this at 1966. The caliber 370 movement looks to be in good shape. Longines had various round watches with rectangular insets on their dials, as well as rectangular watches with round or oval insets on their dials, all around later 60's, earlier 70's. Star is an appropriate case manufacturer, so I would say your watch is definitely original. vintagewatchresources.com doesn't have this particular model but you can look up lots of similar watches from the same time period on that website. There are a lot of "no name" Longines out there. "No name" not being pejorative, but instead indicating a watch that is not a "named" model such as the Conquests, Flagships, etc. This is a fine watch with a good, in-house movement. Pretty nice find for the price! The more common watch in a similar style is a gold-filled rectangular watch with an oval inset, also with the 370 movement. I much prefer yours.