Measured it last night:
Seat tube C-T: 21.25" (54cm)
Top tube C-C: 55cm
It seems to have a bit of everything, in terms of groupset!:
Galli cantilever brakes with CLB levers.
Stronglight 5 bolt single chainset with inner & outer chainguards.
Campag Nuovo Record rear mech
Shimano bar end shifter.
Campag Record LF 36h front hub on Mavic sprint rim with Wolber CX tub (perished but holds air!)
Ofmega SF 36h rear hub on unbranded sprint rim with Vittoria Tigre CX tub (holds air!)
3TTT stem with Primo Extra Giro d'Italia bars (38cm c-c)
Campag Record seatpost & Turbo saddle.
Too small for me, but may fit Ms dhd, who doesn't do CX
Will look into making an Eroica compliant road bike out of it.