Silca pump fit for the frame fit pumps can be guesswork, the spring under the handle varies a bit, here is one example:
A frame with a 485 mm inside measure will take a frame fit pump with a 390 mm barrel length, which does not include any caps or ends when: the Steel Campagnolo head adds about 30 mm with the washer to the tube crotch. the pump handle compresses 30 mm from relaxed to in place, it will compress a bit more, but that is needed to remove and insert. The relaxed pump and handle length of the barrel and handle together is 480 mm.
This frame measures 53 cm center to center with traditional tube diameters, cast Bottom bracket shell.
There is no number on the end of the pump handle of which to assist.
I hope this helps.
John Jorgensen
Torrance CA USA