Leif,
Many years ago, I scattered a couple of Moderately built '50-'51 flathead Ford sixes, when I began to rev 'em over 5,000 rpm on a regular basis. Below that "magic number" they seemed to be pretty robust.
In a supercharged version, I believe the power could be increased, while keeping the engine below critical rev limits. Speed would be gained with the correct gearing, negating the need for higher RPM.
I'd imagine MOPAR sixes would be less prone to self distruct, as they LOOK more robust(to me). However, I doubt if they could withstand RPM in the over 5,000 range, for long, either.
Even the mighty Hudsons were seldom revved much over that figure.
I'd like to see some good research and figures on this subject, myself.
I have GOT to get to Bonneville and see some of the Inliners run! That straight-eight, blown Chrysler had to sound awsome!
