I am stuck not being able to get to my camp and my tractor for a while so I can't pull my bulb to compare. But from the brief searching I've done, the 1073 bulb appears to be the same configuration as an automotive 1156 bulb.
From Messick's parts site this is the bulb from the 2650
View attachment 595243
From the same site this is the bulb from the B3000
View attachment 595244
Don't know if this will help you in your search. Hope it does.
While looking for some other information on this forum I came across a link to this thread on the other Kubota forum.
K7324 Alternator Kit Sourcing? - OrangeTractorTalks - Everything Kubota
In it a B2650 owner expresses his satisfaction with these replacement headlight bulbs.
https://www.amazon.com/gp/product/B017QR53NS/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
RJ -- Why didn't you replace your headlights? They appear to be the same as my 2650 (I couldn't find where it specifically calls them "Headlight Bulb"). If so, I am really pleased with the LED bulbs I put in mine, they are substantially brighter than the stock incandescents and throw a nice, crisp light over a wide area and stay way cooler. $15 from Amazon: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
Will do.....