Same wedge shoe, slightly different mechanism

Thanks for writing in. There's a few possible replacements for these old arrow balances, with the Series 775 being one of them. But I can't say for sure which channel balance is the right replacement without seeing the end attachments of this old balance; for instance, the wedge-shaped shoe of the Series 775. Show us the end attachments of your old balances, and we should be able to narrow down which is the right replacement. Many thanks. 

Thanks for getting back to me. This definitely looks like the shoe to our Series 775, so that's the right replacement option for you. As far as estimating length, is there any way you can put one of your old balances back together well enough to measure out the size you need? If not, I'm forwarding this discussion to my colleague Paul just in case; he has more experience with these balances than I do, and may have an alternative solution. 

Perhaps I can be of assistance. The rod you are holding in your first photo: could you give us the length from the top to the very end of the tube? I should be able to help calculate what you need from there. Many thanks.