The window spring unit has the number 8 printed on it

Thanks for posting. This looks like a 15-177 Pivot Shoe, which uses Series 152 Coil Balances. For a coil spring stamped '8', go with the S152-8 8 pound spring. If your old coil housing is undamaged you can reuse it; otherwise, see the 15-143, 15-144 and 15-145 pieces. These newer components 'sandwich' around the coil spring. Let me know if you have any questions.