That's a 500NE in the bore and a 700NE on top.
[Linked Image]

After cutting off the shotgun barrels, the breachblock/monoblock is clamped in the mill vice and indicated. One hole is indicated and bored out, and then the second hole is indicated and bored out. The bores are not parallel with each other and the mill head must be angled accordingly.
[Linked Image]

Boring out the first hole with a boring bar.
[Linked Image]

Facing the breachblock after boring (not terribly important since the barrels will be smoked onto the breachblock face)
[Linked Image]

Turning the first barrel to fit into the monoblock - tight fit.
[Linked Image]

First barrel into the monoblock.
[Linked Image]

You never pay too much for something, you only buy it too early.