That IS the correct tank. Note the shape of the gas cap - that's a dead givaway. Also note its label - it says OMC, not Evinrude or Johnson. That shows its a late model replacement tank, not an original from the 1950's. I would date this tank at late 1960's - early 1970's. Because its a newer tank its probably in better condition.
The price isn't bad, but not a bargain either. If you want to get going soon, then I'd buy it because of its vintage. If you can wait till Spring, keep looking. Craigslist local is probably the best bet.
I have a collection of those tanks, and will pick one up, just because, if the price is right. I have one just like it and paid only $5, when i didn't really need it. The first tank I bought was $70 (when I needed it now), but it was rebuilt.
This big twin and original tank were not just rebuilt, but restored to better than new...