since it wears a valentino front mech it may have been kitted with a valentino or velox rear one.

it has been nearly forty-five years but i think the silver '69 i saw had something like record front and rear mechs...alas the memories dimmeth!

also assembled a machine for a customer with a model B frameset. he got it bare and it had been resprayed. it was absent chrome and transfers so not of much assistance here...

if your example a 1970 one would think it late enough to have a 70mm shell rather than ye olde 74.

iirc the changeover year was ~1967...but of course the cino experts will know better.