Trying to ID my Omega

Hello, I am new to Omegas and to this site. I was recently gifted my grandfather's Omega. My grandfather is long deceased and no family members know anything about this watch.

I want to know the year of manufacture, the model, and the metal of the case. This is what I have learned so far (and pics are attached):

The eight-digit serial number begins with 17, which I think means it was made in 1960. Is that correct?
The caliber is a 600.
It appears to be 14k gold, but that isn't noted anywhere.

There is no model name on the dial, and the numbers inside the case probably help decipher the model -- but I can't seem to do that. Inside the case it is stamped like this:

PN6615
118554

Thanks to all!
Dan

Almost certainly US Collection based on the PN6615 case number. Likely 11/16" (17.25mm) lug width.

Please post a photo of the inside of the case back.

I have a poor, nearly illegible photo of the case back. A local jeweler has the watch, which they are sending off for cleaning and service. They took the case off for me and wrote down the numbers I posted before. I took a photo with my iPhone, but it was lousy and I didn't realize it until I left. Anyway, see attached. Thanks.