Capitalism is defined as an economic system where private property over the means of production exist, and it's characterized by wage labor and the profit motive. This definition sounds marxist, and indeed it is, but it's widely agreed on — even though there are more specific definitions, these points are something most of them have in common. Fascism, or corporatism, doesn't change any of these things, it can't be considered its own mode of production. Else, you would have to agree that Social Democracy isn't capitalist, because the economic ideas between Fascism and Social Democracy don't differ a lot.
The problem with Mussolini is that he changed his ideas on some things like he changed his uniforms. And boy, the guy had tons of uniforms. This is what makes it hard to make an accurate description of a fascist-esque economy.
Social Democracy has its roots on socialism, too. So much so that several social democrats today still overlap with reformist Democratic Socialists. For more than half a century social democrats agreed in building a socialist society by gradual reforms; it wasn't until World War I and the split of the Second International that Social Democracy changed to mere reformism. It is because of things inherent to that split, too, that Mussolini abandoned socialism... although the split of the Second International could require a thread on its own for how complex it was.
They weren't fascists in name, but they did share many practices in common with truly fascist regimes, like militarism, nationalism, belief in stong national security, social conservatism, suppression of political groups, class collaborationism, and some more depending on the country. The last Argentine dictatorship, for example, created many social plans. They also killed our heavy industry, but made business easier for private owners by paying them. It's not uncommon these days to see an upper-middle class moron shilling for the dictatorship to come back.