Thanks for reaching out to us! This looks like our 15-177 pivot shoe to me. I recommend the Series 152 for the coil springs. If there aren't any numbers stamped on the tongue of the spring, you will have to divide the sash weight by the total number of springs in the window.
I'll be here if you have any questions!
No, the Series 152 springs screw to the side of the shoe instead of hooking into it like your old one but it should still work.
If the sash weighs exactly 11 pounds, I'd recommend using one S152-6 6-pound spring on each side of the window. This would total 12 pounds of overall support which should be fine so long as the weights are within a pound of the sash's actual weight. We also sell the 33-072 screw separately which can be used to install the spring to the side of the shoe.