One window, two sash, 2 - 15" white springs Balances and 2 - 17" spring balances

Hello there!

Are the outer tubes for these balances 5/8" (or 9/16") in diameter? If so, I recommend our Series 500 and the 17-012 bracket that is sold separately. I'm confident our modern balance will work for you as long as your outer tube diameter matches ours. You'll just need to weigh your sash on a scale to determine the appropriate color tip option for your replacements. 

You can use a #8 screw but the length will be a huge variable. You'll need to use your best judgment on how deep you think you can drill without hitting the glass. With old window sashes like this, it's always going to be different. 

I hope this helps!