Originally Posted by T-Mar

Thxs, the crankarm code helps. The crankarm itself was manufactured November 1971, which would be appropriate for a 1972 model year bicycle. It also increases confidence in the frame manufacturing date being May 1972. Japanese manufacturers typically started building the new models around September. This allowed them to build up stock and allocated time for trans-oceanic shipping, customs clearance and channeling through the USA distribution system, yet still have the first shipments in shops for the lucrative Christmas season.

I am still curious that the serial number format uses the Japanese Imperial Calendar and wonder if Katakura transitioned and changed their format around this time. To this end, I would appreciate if you would check the branding of the handlebars. Early Nishiki racing models manufactured by Katakura typically used Nitto handlebars that carried a Nishiki Road Silk designation. Silk was a Katakura brand, so their presence would increase confidence in it being a Katakura manufactured frame, like the slightly later Professionals. It's unfortunate that the decals have been removed, as Katakura manufactured frames also had Silk designations on some decals.

Regarding the saddle, specs were notoriously sparse during this era. It was rare to mention the brands and models of major components like the derailleurs, cranksets and brakes, let alone secondary components like a saddle. Early Nishiki racing models typically came with a narrow saddle having a plastic base covered with a layer of foam and a leather cover. I've seen both Elina and Tahei brands. Having said that, 1972 saw the biggest sales jump in 10 speed sales, with demand outstripping supply. Consequently, substitutions due to shortages were not unknown, though the Japanese seemed to suffer least in this area. If the current saddle is a Japanese brand,then there is the possibility of a factory substitute but if it is not Japanese, then it is almost certainly a post factory replacement.