Correct choice

Replacing channel balances and retainers clips in old Jordan windows (house built in 1991). Appears the best choice is Series 390-29 Option 2840 at 29". Retainer clips are #16-002. It appears one window has original balances with stamp in metal of: 28 4c J Second window balances appear to be replaced with ink stamp of 28 4 FN Caldwell. Measurements are the same as your pictures. Only difference is on the foot insert-the longest side that goes outside the channel (part that is 1" long) that splits so it can slip into channel-its opposing side that goes inside the channel is longer than pictures. Instead of being same height as rest of piece that slides inside, it continues on to make a leg (like top piece). As I'm replacing entire balance, does this matter? As indicated, everything else is the same. Also, is the 2840 the correct weight?