How would my fiance and I arrange to use my grandmother's engagement ring?

My grandmother passed away three years ago. She didn’t specify who most of her jewelry should go to, and her engagement ring was given to her son’s wife – my mom. My mom then gave it to me because it was too big for her and, I think, because she thought I ought to have it.

My guy and I are about ready after eight years to get the wheels in motion on the marriage thing. So I’ve been looking around at rings for the last few months – only none that I’ve seen is close to as breathtaking as my grandmother’s, and obviously they’re not as meaningful. The ring is as much a memento of my grandfather as of my grandmother – he was the jeweler as well as the groom.

Is there any graceful way we can go about putting this ring in a position to become my engagement ring? I know “the grandmother’s ring” is usually from the groom side, not the bride’s, and I think I’ve figured out why – the logistics. Would I want to get it appraised, give it back to my parents, and then my fiance would buy it from them, or some other such awkward arrangement? Or am I overthinking this, and we should just declare it my engagement ring and I’ll start wearing it on my left hand? I don’t want to give the impression that I’m using it just because it was convenient or free. Is there any good way to allay this concern?