Swish had a typo which makes his comment a little confusing. The GMT 16750 was a GMT MASTER not a GMT II. The first GMT II was the 16760 as Swish mentioned and it arrived during 1983. None of the GMT 16750s were GMT IIs.
Additionally, there were no GMT IIs made during 1978.
If you go to the GMTforum.com, there is a thread there comparing the various GMT and GMT II models which would be quite helpful if you are fairly new to the various Rolex GMT models.
Here is the link:
https://www.gmtforum.com/viewtopic.php?f=3&t=265