How to determine a safe red-line?

To have 10lbs. Per 1K RPM's would be great but is not a mandatory thing. If you have 20psi at the finish line, your good.

You can safely put a red line for your engine at 500 rpm above the listed RPM range of the cam from the manufacture. (Though a 1,000 shouldn't be a bad thing for the engine.) The reason is rarely win you make more power above that and it would be a waste of time to exceed that.

The best red line guide is where the valve train floats. Meaning, the valve springs can no longer control the valves well enough to keep them where they belong when they belong there. That will normally happen well past your power making point.