Admittedly, the 600hp+ 440 based motors I've tested all had cams with more duration than the hyd roller TF used in their build, so they should be tuned to a higher rpm.

That being said, I've also found that at that power level, going from a 2" x 3.5" header down to a 1 7/8" x 3" header(hooker 1 7/8" super comp in this case) would cost some power. It's just one element that's makes me question the 620hp number.
I'm not saying that's not the number they saw from their dyno, I'm just questioning if that's the same number I'd see from the same build.

The horsepower tv 505 used the TF heads and intake, and a bigger cam than the TF cam, and only made about 20hp more.

I'm thinking if I pulled that TF top end off a 446 and bolted it onto a 505, then swapped from 1-7/8" headers to 2" headers, added 10deg more duration and .050" lift, I'd see more than a 20hp difference.