In a big block that .528 is a guaranteed 11 second combo.
If that .590 cam is running out of steam after 6400 I'd be looking at the heads. That's plenty of cam. That .528 cam is still within 5% of peak power at 6400 RPM.
He's running MCH ported Eddys 440 port size, 320cfm@600, been trying to persuade him right or wrong to buy my old CC.650 solid for $150 that I ran in 1990 in the blue Cuda.....he's at 12.7:1CR