Very impressive design, I think you got pretty close to the original image.
As for who might use this thing, I have a few ideas. Since this is an older design, whoever built it (to me, the hull color and weaponry gives it a distinctly Britannian flavor, but it could be almost anyone save for the Scythians and Immortals) has likely upgraded to bigger and better designs by now. So the surplus Nocturnals likely trickled down to lesser powers (as part of trade deals, being bought for scrap, etc). So any of the minor powers might have a couple of these things floating around their shipyard by now.
"There's suspension of disbelief and then there's insulting my fucking intelligence"