Need help identifying a 15 inch block/tackle balence.

I'm happy to give additional measurements as needed. The calipers are very cheap and I only used them to get a rough estimation.

This came out of a small-ish window. The cord frayed and broke off of the hook/clip that kept the balance anchored to the frame embedded in the wall. The aluminum channel is 15 inches long, 1/2 inch wide and about 3/4 inch deep.

The markings:

1420 (weights, i think)
BSI (manufacturer?)
AL (Aluminum, i think)

It looks like a 15 inch block and tackle style with a rating of `1420`, but the plastic ends are what I'm having trouble identifying. They don't seem broken, so can I just move them to the replacement? They don't appear to be riveted in