Balance Replacement
We should be able to help with this, yes. The first thing we need to do is determine the proper size and spring calibration. For size, the rule of thumb is to measure the height of the visible glass and then add 1". So, for example, if the visible glass is 20" high then you want a 21" long channel balance.
For the spring calibration, you would need to weigh your sash on a scale and get a precise weight. We have a chart on each balance store page that you can then use as a reference to pick the best stamp option, which is what indicates calibration.
Finally, we need to determine what the Series is, which is based on the combination of nylon fittings. I've narrowed your balance down to two possibilities: either our Series 351 or Series 390, depending on the depth of the bottom shoe. That's the only difference between them. I recommend measuring your shoe and referring to our dimensions to confirm the best match.
I don't have a tool to measure the sash scale. What is the most common one ordered? It is rather hard to pull the sash with pliers.
I'll be measuring the bottoms shoe to get a better idea of which series it is.
I'm afraid there isn't really a "common" stamp option. I would highly advise against going that route, anyway. These are very delicate systems and their springs are only designed to hold a very specific weight range. If your sash is out of that range by even a pound then your balances will simply not function properly. Either they'll be too weak and you will struggle to open the window, or they'll be too strong and you'll struggle to close it; if it's especially strong then the window will even open up on its own.
I know it's a hassle, but you really do need to get the exact weight of the sash. Ordinarily you could just use the stamps off the old balances to pick the right option but since yours are missing you don't have a choice in the matter. It has to be done.