I don't recall what the differences ARE, but I can touch on the WHY.
The nosecones on the heros were separate parts (covering a mounting point) that had been cast and then hand-cleaned. They all came out a little different due to the by-hand attention.
One hero, with nosecone in place, was cast in L-R halves (as opposed to the top-bottom construction of the heros) and that mold used for the pyros. For whatever reason the nosecone on that hero was atypical, so all the pyros ended up with a nose different than most heros.