Inherited omega deville

Hi, I was left this omega deville by my grandad a few years ago. I've worn it quite alot and have noticed it has a replacement aftermarket strap. I have tried to find information about it on various websites and even on omegas vintage database but never found the exact one. I actually found these pictures on an old Facebook post, however this is exactly the same as mine. Can anyone give me more details on it? Etc the actual year and what the original strap looked like? Thanks.

Hi, I was thinking late 70s. Thats great thanks for your help.