There is no question these western technologies falling into Iran's hand have been a blessing. I recall General Hajizadeh stating that the engine they recovered from RQ-170 would propel Iran's technology in this sector by 30 years. Technology is technology, where it comes from does not matter, the more shortcuts we can find the better. In terms of how Iran manages to reverse engineer, we need to keep in mind that Iran has a very robust underlying science and technology base that can help it in this regard. There are teams in Iran dedicated to just such a thing.
I have said this before many times and we need to always keep this in mind. Iran had lost centuries of development, what we have managed to do in the last decade alone has been nothing short of extraordinary. In terms of military hardware, regional influence etc, we have done things in a decade that others needed decades/centuries to accumulate. There are still many areas we need to fix, but despite the problems we faced, Iran is still leaps beyond these other regional states. No wonder they're scared to death of Iran. Unfortunately for them, they have seen nothing yet.