318 safe max RPM?

Like I said I am not to worried about the top end. It should be fine. 273 heads, extensively ported. 360 valves. And Edelbrock RPM springs. 273 adjustable rockers.

Just wondering,
If they have such oiling problems over 6,500 how did they spin those D-stock 273's so fast? I have read accounts of shifting at 7,000

Just wonder what mods they may have done to keep them together at that speed. As my next engine will be built to hopefully duplicate, or improve upon that.