The traditional understanding is communism as left wing, and fascism as right wing. Certainly the stalinists used the terms in this way. You are right in pointing out that there is little effective difference between the two.
As a way of differentiating the two, communists generally espoused an internationalist philosophy whereas the so-called right-wing fascists tended to be extreme nationalists. But even that is rather unsatisfying as both use nationalism when it suits them and both build international alliances when it suits them.
Communists leaned toward total state control of the economy, whereas fascists tend toward state control of owners, but this is a pretty nebulous distinction.
The important thing to remember is that the left-right distinction between the two is mostly propaganda, as you rightly point out, they are but two sides of the same coin. The problem comes in when American conservatism is referred to right-wing, implying that somewhere on a continuum between one kind of totalitarianism and it supposed opposing twin, you will find crew-cut Republicans, and this is a mistake. Its a mistake when the totalitarians say it and its a mistake when American conservatives allow themselves to be drawn in to using such language with respect to themselves.
American conservatism is a thing of its own. We are no where on any continuum between Stalin and Mussolini, we have nothing in common with either of them. Half-way between total state control (left) and total state control (right) you will not find John Locke and you won't find Jefferson. We are neither "left" nor "right". We are something else entirely.
Halfway removed from totalitarianism would be, in my view, the mixed economies that make up most of the world. Some are more free, some are less free, but none of them have any clear philosophical barrier separating them from Chavez and Castro, though they might like to believe otherwise.
My reference to Chavez having combined "left" and "right" was a reference to his combining Marx with outspoken Venezuelan nationalism and pan-latin nationalism.