I think it’s a fake, Omega didn’t stamp the gold content on the outside of the caseback, it’s usually on the inside. Also I don’t think they put antimagnetic on the dial, but I maybe wrong with that. More knowledgeable members will comment shortly.
If you get an honest/competent watchmaker to assess it they will tell you:
it doesn't have an Omega movement
it is not 18K solid gold
it is probably a "highway gold watch" prominent in Europe in the 1950s/1960s
It is worth nothing
You will never see an Omega watch with angled off-set lettering stamped in. This was made by a blind Man or some bone- head that flunked grade 8........ 5 times.