An underside shot of the fork crown might add detail. If the crown is stamped/folded/welded there might be visual evidence of the seam's welding. But lacking the visual cues doesn't mean the crown was cast, it could have seen file/finishing to hide that.

Sorry but I just don't see the value to spend the time it takes to add a layer of material, shaped and then finished to what the photos show. To mill out this is also a lot of time/effort and with the non straight edges of the top surface feature any machining would likely be from a CNC machine, not the most common tool for a builder to have today, let alone back about 40 years ago.

Admittedly there are builders who do very creative features with very little machine tooling (to quicken the production) and/or who don't see their time as a big deal Andy