Hello,
The old style rod balances shown in your photos are no longer available but the new style S770 channel balances should work as replacements as long as you replace both sides. Also, you would round down the length for the S770-16, S770-20, and S770-27 balances.
It is a bit strange that the other two balance measurements differ from the standard 1/2" length increments used with these balances. We do offer the S770-28 and S770-29 balance but we can't be sure which would work best since the length differs from the standard measurements used for these old-style balances. I'd recommend double-checking the length of intact versions of the 28-3/4" and 27" balances to confirm the correct replacements.
You'll also need to weigh the sash for each length option to choose the corresponding strength options. There is a chart under the balance product descriptions that will show the weight ranges supported by each option. Thank you!
See the image below showing the cap-to-cap length measurement you'll need for these balances.
