29" balance with 2840 spring

Thanks for posting. Does the balance's bottom fitting, or shoe, lack 'wings', or side tabs? It's admittedly a bit tough to tell in your photos. See the diagram below for reference.

Diagram on how to choose between the 15-001, 15-002, 15-004, 15-005, and 15-029 channel balance shoes.

Assuming your balance's shoe lacks wings, this is either the S351-29 or S390-29. The only difference between these two balances is the depth of the bottom nylon shoe, or the 'heel-to-toe' measurement. See the diagram below. Compare both with your old balance to see what matches best. In either case, for a new stamp option choose 2840.

Comparison of the S351 and S390 balance shoes.