This is the model PX of Katakura SILK which was produced in around 1970s.

The factory of Katakura bicycle was located at Fussa city, and it was near Yokota air base of US air force.

Back in those days, Katakura bicycle industry accepted the order of this big model from US air force.

Spec

Tubes: KATAKURA original CrMo tube
Frame end: F/100, R/126 mm
Seat tube length: 625 mm (C-T).
Top tube length:575 mm
Brake: YOSHIGAI Dia-compe Center-pull brake
Brake lever: YOSHIGAI Dia-compe mod.144
Btake lever Pad: Leather Handmade
Handlebar: NITTO B105 400mm
Stem: SAKAE Apex-AH Forged Super Duralmin Model, Extension/80 mm, Diam;21.1 mm (Special size)
Seat Post:SAKAE CT
Saddle: **
Shift lever: Suntour VX
Front derailleur: Suntour
Rear derailleur: Suntour VX
Cranks: Sugino Super Maxy
BB shaft: Sugino Super Maxy
Pedal: Kyokuto Pro Vic II
Hub: SANSHIN
Rim: UKAI 27ing*1-1/2
Tire: PANARACER
Chain: SHIMANO HG40
Freewheel: SHIMANO 600 6-speed
Front carrior: YOSHIGAI

Nowadays we can not see this model even in Japan. I suppose model PX might be produced as "build-to-order manufacturing".