There's something called a "down stop fitting pad" that I've never encountered before. It's an oversized part of the blocking lug that you can fit to account for oversized frame cuts. I had to file in this place so that it would fit inside the frame with the hammer and sear removed. Then it was regular fitting on the blocking lug as usual.
https://www.harrisoncustom.com/image...une%202016.pdf
It took an extra 10 minutes to figure out and fit, but the end result is -exquisite-
What a part. Oh man. I want everything they sell now.