Without seeing what you have it could be that you have a 74' headtube with a 72' stem as your replacement. I don’t recall Custom having a standard bolt.

The custom stem has a recessed allen bolt with a wedge expander. The Royal that may have a conical expander, I can’t recall.

The main difference between the Custom stem is cast, the Royals are forged.

The Royal is anodized and the Custom is not.

A track stem would have more drop than a road.