Safe max RPM for bone stock 5.9 magnum

I never even pulled the pan.... she's running 13 flat in a long bed D150. I've done nothing but pound out of town and at the track since installing. By accident I hit 7k when the tires broke loose. Mild regrind cam and Hughes spring kit.
A flat 13 seconds with a stock long block other than the cam,no cylinder head work? That's impressive.