According to the dial design I´d say it is a 1964 LeCoultre wth 17 jewels Valjoux 72 (see for more info on LeCoultre chronographs: Wolfgang Salm, Battenberg editors, ISBN 3-89441-376-X).
This is quite helpful. Many thanks!According to the dial design I´d say it is a 1964 LeCoultre wth 17 jewels Valjoux 72 (see for more info on LeCoultre chronographs: Wolfgang Salm, Battenberg editors, ISBN 3-89441-376-X).