In need of correct screen frame size and mounting hardware

Curious if you may offer some assistance. We have numerous double hung windows upstairs, I believe that they are Crestline. They are aluminum clad exterior and wood interior. There have never been screens mounted to the windows, evidently the original owner was to tight to purchase them. There is a groove that is 3/16" wide and approximately 3/16" deep that runs vertically on both sides and horizontally of the top of the exterior portion of the window near the exterior stop.

I was originally thinking that 70-009 push pins and some 7/16" frames would do the trick but there is only about 3/16" on an inch available from the stop to the beginning of the groove, so there is not a lot of room. Any assistance would be greatly appreciated, these windows are upstairs and we literally run the AC on a nice 70 degree day since we cannot open any windows. Thank you so much!