Any significance in strength between stock 360 cranks and the cast aftermarket 360 -

Like MRL says. Sometimes it makes $en$e to use a new part even if you have "good old" stuff. In order to have a crank properly done for my builds, I will spend $250-$300 on it. For another $60 I can have a new one that is stronger, more performance oriented from the start, and finish-quality wise almost as perfect as what my grinder gives me back.