So, I just bought a 543...
I’ve dyno tested a few stock appearing 526’s(4.375x4.375) with exhaust manifolds on them.
Peak tq in the 42-4400 range, peak power in the 6000-6200 range.
They are very responsive, and will go to 7k without hesitation.
With the bias ply tires, they’re quite a handful on the street.
They have gone over 130mph in the 1/4 at 3900lbs on those tires.