@DavidJay
All the numbers that can be seen do match, I'm sure it hasn't been re-blued, as my Folks got it in the early 60's.
I did look at Simpsons, they only have one BYF 42, listed at $2495.00, but it also says "Rig, includes an original leather holster, dyed black, proofed on the back eagle/WaA145 next to a date which appears to be 1977?. Also includes an original unmarked takedown tool and an extra magazine, an unmarked wood bottom variation.
Also it notes 85% wear and "fair bore".
Dang, I thought I'd see several listed to get an educated guess