The other bad news....

I can't figure out what receiver sight fits the alterations in the rear of the receiver.

Anyone be able to help ID what receiver sight would fit this?

Here are the measurements as I have them:

Has two horizontal holes D&T'd for a receiver sight; hole measurements are 0.60" outside to outside; 0.345" inside to inside; about .470-ish" center to center. Overall width of the receiver sight "base" is 0.840".