Most Vinyl windows of that age used spiral balances, only a few companies used (Spring) bock and tackle. Bock & Tackle balances were common with aluminum windows.
Both are still available, to determine which system you have tilt in bottom sash and look at the side frame. If you see a spiral rod that goes into a tube,it's a spiral balance. If you see a thin sting, it's a Bock & tackle.
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