"A model that doesn't exist" is always a difficult statement to make about Grecos, given that they ran a custom shop-like operation starting in 1972. There are countless weirdos, oddballs and unicorns out there (I know, I have a few of them), built for distributors, retail chains and end customers. But having said that, this one looks so close to standard SV-800 specs that it's kind of hard to imagine what they could have added to merit more than doubling the price? Legit Gibson pickups, possibly??
Otherwise, a forgery attempt seems somewhat likely, the 1 seems to be squeezed into the space the original writer would have left between the dash and the 8. On the other hand, that would be pretty hard to do through an F-hole...? You'd need a steady hand and a good eye for colour matching. But who knows?
But I personally wouldn't be prepared to pay more that the going rate for an SV-800 for it.