I work in ag stuff, so thought I'd check out aftermarket bearings for your hotrod (like Fafnir, Timken, etc).
Bottom line, bugger! I can get part no. 30205, which is 25mmIDx52mmODx16.25mm tall, but that means reaming out the headstock to suit, or you could use the XL250 brng set, but that means shimming up the headstock with 0.75mm thick tube, so haven't been able to help, sorry man.
At least you know what your up against now I spose!
Did something similar years ago, and reaming out the headstock, then fitting a machined-up inner pipe to restore strength was how I went, but I'm sure you know what you doing man.