The difference between the Two handed sword and the Polearm, from a rules perspective, is in whether or not it has a open cell head attached to it.
That and the length, both the overall length and the grip size. There is some overlap for the overall length, but only two inches. And of course the grip sizes are maximums only, so there is overlap there.
So if you made a 61" long weapon with a 40" long "blade" section. It could at that point be confused for either a polearm, or a two handed sword. However, as soon as you either put or did not put a foam head on it, it would become either a polearm or a two handed sword (or two handed blunt, depending on how big the head is).