It's a slim. Definitely not a Faboy. They shave differently. Fatboy has a milder head which some (I) prefer but they tend to be a bit pricier than Slims. I think more people would prefer the Slim's shave though.
Not sure how the seller has narrowed it down to 1958 without posting the date code for us to verify. D (1958) to G (1961) as opposed to H (1962) to N (1968) for the Slim, I believe.