Hello,
Unfortunately, the corner shown in your photos is no longer available. Take a look at the 95-218 corner key used on Silverline window screens. This might be the only option that could work for your 7/8" thick screen frame. You can remove the slide latch if it gets in the way of the window frame. Most screen frames today have a 3/4" wide face. Take a look and see what you think. Thank you.
I have known some customers who have tried cutting the screen frame a little to accommodate the larger face on the 95-186. The legs on the corners seem to be the same size, so they should fit into your existing screen frame. As for a pull tab, you could use the 70-128 if that's all that is missing from the screen frame. As for the miter box and hacksaw, that is what I would use to trim the frame down a bit. Please note that each cut will need to be precise for this to work.
