The combination of modest compression and cam timing, combined with a small port cross section(relative to the displacement), doesn’t seem like something that would lend itself to an extended upper rpm power curve.

Assuming the valvetrain was 100% stable to say 62-6300, I don’t think the engine would peak above 5800-ish even if it had a Super Victor and a Dominator on it.

But....... there would be only one way to know for sure.

And then, what would the bottom end of the curve look like with the SV/4500 in place?

However, that’s not to say that as it was on the dyno you didn’t have two issues contributing to the poor upper rpm power.
Valve springs.........and possibly the manifolds tuned rpm.
If the curve would have hung on even just a few rpm longer, it could have been worth 20+ hp........ and even more in the 5500 range.