I have a 1995 mustang GT and have had the engine rebuilt, using all preformance parts. Say nothing else where to fail anyone have an idea how much horsepower it would or has taken to break a stock crank or spin a bearing in a 5.0.
I have seen a stock crank take 650 H.P. Was I lucky? Yes, very. Yours may not take that much H.P. It may break at 350 H.P. (not likely) or live at 700 H.P. (maybe one time) It so much depends on all of the other prep and machine work and how the power is made and used. There is no way of knowing for sure as each and every engine is different, and each and every crankshaft is different in some small way. I would venture to say that you are safe up into the mid to high 400 H.P. mark.
I know of 3 people personally that have been just at 500 RWHP or just over with stock cranks. They were all on 91-93 LX Mustangs. As stated the block will probably let go before the crank will.