Block and tackle balancer

I agree this is a Series 751, but there's a few things to clarify:

• Is the metal channel 24" long?
• I agree the stamp code is a bit unusual. If you obtain the exact weight of the window sash, that will tell us what stamp option you need. 
• Can you give us an up-close picture of that bottom knife-lock shoe? The Series 751 can use a few different ones. It comes by default with the 15-014, but there are some variations. I'd like to confirm which you need. Make sure it's an undamaged version, if possible.

I talked it over with my colleagues, and we think our standard S751-24 with its 15-014 shoe (which comes included and attached) should work as a replacement. You'll need a stamp option of 23R, for a window sash in the weight range of 10 through 18 lbs.