Watch identification assistance required!

[airboy85]

So here it is, a piece that was given to me by my late grandpa many years ago. I have decided that it is time for me to bring it for a complete overhaul. But as I am quite a novice in Rolex's line of models, I am hoping that the experts here could lend a hand in helping me to identify the model (and if it is real or not :X ).

I believe this watch was from the 70s - 80s? Oh and its a manual. Also, the acrylic has a small chip at the bottom. Is it replaceable with a modern sapphire crystal glass?

edit: after reading another recent post about a watch identification by another forum member, I believe this is a variant of the 1500?