27 year old Kolbe windows need new channel balances

Thanks for writing in. I see you were looking at the Series 751. Are you certain that's what you have? If not, please remove both sized balances from the window and show us pictures of all attachments. Confirm the length of the metal channel on both balances. To be safe, I'd obtain the exact weight of both window sashes; sometimes the stamp codes aren't always reliable with the ribbed tilt balances, so the exact weight of the window sashes will tell us the stamp options you need. Many thanks.