My take,
Reference number on inside case back will help you search on what movement was originally inside. Could be a movement ring which might have to search for or friction fit into the case back.
Since the movement was swapped out. Dial posts may have been cut off as dial looks a bit off center, so maybe new posts solder onto what appears to be a gold dial.
Now the big decision
Wear or not wear.
Not. leave as is and stick it in a drawer. Mostly worn by older men in later 70's/80's
To make useable
Have the bracelet cut off by an experienced goldsmith. Have new lugs created (Omega De Ville design) and soldered onto the case for use with a leather strap.
Get an estimate. Maybe swap the leftover bracelet in exchange for the work
Could possibly have posts also soldered on by the goldsmith
Caliber is most likely an Omega 620