Originally Posted by juvela

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Final year for foil transfers was 1973.

This model of Simplex Prestige rear derailleur was last produced in 1969.

The white Delrin shift levers are another dating aid which moves the machine into the 1960's as well.

Guessing perhaps somewhere near to 1968-69.

The 61 marking you found on the bicycle's BOCAMA head lug refers to the angle in degrees between the lug's sockets for the headtube and downtube.

Some Simplex rear derailleurs bear a date mark on the back side -



The bicycle's wheel rims are likely Rigida SUPERCHROMIX. These have a diamond symbol next to the name.

There is sometimes a date inside the diamond:




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