Hole spacing for a Lyman 21

[Keyhole]

Does anyone know the hole spacing for a Lyman 21 sight? I have a model 99 that has been tapped but it does not appear to be typical for scope mounts I've seen. The holes are about 2.5" apart.

[Mad Dog]

To close for a Lyman 21. I'm guessing the holes are on the side if your asking about a Lyman 21.

Wondering if maybe it's for a Pachmayer scope mount or another side mounted scope mount like a Griffin Howe.