Does the Mark ii dial have the words "Swiss made" at 6 o'clock? I have seen some with and without. Based on my bit of digging, seems like most with the words are from the early 70s. Did Omega later remove the words? Below are photos of 2 watches.

 

They should all have Swiss Made. Original vintage ones will have the bracketing T's too.

 

The first picture was simply taken at an angle, so the tachy scale covers the text.

 

@timestamp is spot on here.