https://thegreatmodel8.net/

I seem to remember reading somewhere, maybe here, maybe in the Model 8 book, that when a Model 8 was sent to Rem for repairs, in the time when the 81 was in production, that they might upgrade that model 8 to an 81 configuration.

Sound plausible or am I misremembering things in my aging brain?

I have a couple with 1950 Bbl sleeve codes that are 8s, with the caveat that 81 parts were used in the place of original 8 parts.