Authentic finish (hot dipped blue) contact Steve at two rivers arms in OK.
Personally I cold blue mine using blue wonder.
Looks like this when done in two passes (blue, develop, oil, sit for 24 hours, clean, and repeat).
Doesn't penetrate as deep as the hot dipped blue but super easy to apply, and inexpensive with pretty good results.
And Yes, that is a re-weld of 4 pieces from the original front, and rear stubs with a cut demilled receiver used to produce the center repair section.