convert push out casement window to winder operation?

[ubeaut]

is it possible to convert my 1920's timber casement windows from their current pushout stay operation to a winder mechanism? The stay is attached to the middle of the vertical edge of the window and i think a winder would need to go on the base of the window. I really want to be able to lock the windows open and to install a fixed timber flyscreen to the windows and can't with the stay operation as a) they dont lock and b) the stay juts inside the room when the window is open. installing...

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