39-253LB or something else?

Thanks for posting. This operator is definitely unusual; we don't have a type with that type of bracket at the end of the straight arm. The 39-253LB uses the 39-529 square slider, sold separately; while the 39-438B uses a rectangular track slide that comes attached to it. I am forwarding this discussion to one of my senior colleagues who is an expert in casement windows. I want to see if either of these mentioned options could work for you, or if he has any other solution. Thanks for bearing with us. 

Perhaps I can help. I do recognize this operator, and it's a kind that I believe is no longer available. I suggest taking a look at the 39-253LB. I think you could use this operator and the 39-529 slide. However you must first see if you can install the 39-528 track on your window sash. If you can, then I think you'll be okay. Take a look the 39-253B along with the related parts and videos.