Do you sell this old window opener?

Thanks for writing in! I believe you may have the 39-060 Keller Window Crank. The opposite handed operator is the 39-061. 

Like yours, this operator has an offset top installation hole and a 2-1/4" arm extension with a 1/4" - 20 thread. Take a look over the dimensions and compare them to your existing operator to confirm if this is the correct replacement. 

This operator uses the 33-070 5/16" Shoulder Screw.

Dimensions for 39-060

Alternate view of 39-060

Given the closeness in the dimensions, I do believe this is the right fit. These are the closest match we have in terms of design and dimensions to your existing operator.

Just to be sure that this is the right fit, can you please provide a photo of the inside of the operator, from a front-profile view? I would also suggest double checking the dimensions.