Anderson casement 1960's or 1970's vintage

The Andersen window operator can be replaced with the 39-095 Andersen Straight Arm Operator. The opposite version of this operator is the 39-094. Based on the measurement of your arm, I cam confident this is what you need but be sure to double check the dimensions.

The 39-286 handle is sold separately from the operator and track kit.

Dimensions for 39-095