YD-A as discovered
Here is the frame of YD-A frame number YD21 as it was found. It can be seen that a fairing bracket has been welded onto the headstock as per the 1961 Factory YX24/ RR250's and Yellow Tanker models. These were first seen in the US in Feb '61 when Yamaha brought over Ito & Sunako to ride in the Daytona GP. This bike also has engine mounts added from the same model, showing that the bike had been adapted and raced by a during this period and this work must by someone with considerable Yamaha experience and availability to spares, ie. Sonny Angel.
Frame number YD21 is stamped onto the frame downtube.
The headstock shows YD-A stamped into it. Note, the original grey paint is clearly visible under 2 layers of black paint.