How to determine a safe red-line?

Stock cast lower parts I would never rev over 5500. Dont care what valve train you have. Cast parts are weak. If you want to rev to 6500 and up forged is a must. 5500ish is my limits for cast parts. A touch over wont hurt.

Remember the tug and shove of the rods big ends. Even a good rod bolt is only good at the clamp not at the center of the cap.