Here’s a similar build:
Flat top 446, sidewinder heads flowing 290(same casting as the Toth head), 250/254-108 SFT cam with Chevy lobes, 1.5rr, rpm, 850DP carb, 2-2 1/8 x 4 dyno headers.
Notice the difference in VE, and bsfc.

I’d like to see the sheet from the best run.

If your motors is still on the dyno or if you want to test the cam theory, try adding .006 tighter lash for tree pulls and then loosen it .012 for another set of pulls. If it makes more power with tighter or looser lash then you have some insight on the cam, looser makes more change it to smaller duration, if tighter makes more power change it to bigger duration and lift
What is this motor going into and what is its application?
As far as total advance I've done a bunch of testing at the tracks and on engine dyno, every 440 type BB Mopar I've tested like 34 to 36 degrees total VERIFIED timing which MSD ignition box are you using? THat old Accel coil may not be your friend if your using an MSD multi spark box
Lean is mean, FAT is NOT
I've had similar stock stroke motors with less compression and bigger cams with smaller heads (lightly work over 906 iron heads) make more power than yours did, but if we are not testing at the same dyno with very similar weather conditions then the results can't be compared due to the weathers effect on the motors.
What brand and heat range spark plugs?
How about posting another dyno sheet with a pull up to 6000 RPM? That will help me maybe be able to help you a little more
I've seen a lot of my similar built BB Mopar engines peak under 6000 RPM on the engine dynos (three different brands and locations) also, but they all went faster at the drag strip shifting them higher
Don't give up, finding the right combination is the key to success in every venture in life, as well as in making more HP and going faster than the other guys scope: up:

Did you get any vacuum readings during the pulls?

Those are good numbers, especially with the large headers!

190 psi cranking sounds in the ballpark for those cam specs. I still don't understand the BSFC numbers. The best cam I got for my 540 wedge was from Jones cams https://www.facebook.com/Jones-Cam-Designs-173457799374053/

The other issue to investigate would be the heads. I have seen heads that backed up, flowed less at higher lifts, and they just killed the engine. Sometimes you have to flow them at 35 inches or so the catch them doing it. I have seen some CNC programs that backed up so don't think all CNC programs are perfect. Usually, a little grinding on the short side will straighten them out. I have messed with big block mopars a lot and most like 36 degrees timing. If the O2 numbers were calculated I would trust the color of the plug more than the calculations. Did they try leaning on the jets? I still like exhaust temp readings as well, many times a cam not right will give you high exhaust temps. If the exhaust ports are dragging out part of the fuel charge at high rpm during the overlap that would give you the poor BSFC numbers, and usually exhaust temps will be high as well.

Has TDC been checked for accuracy?

A lot of people here are questioning the timing. Add me to that list.

It's interesting to run through a cfm calculator of a 446 at 4000 rpm to get 567 cfm at 110% ve and see the dyno sheet at at 118% with a lower cfm number of 556.
Do they backup their Wideband a/f with another one? Sometimes the sensors are off by quite a bit due to being dropped or fouling. . I back up my dynojet WB with a Motec WB when looking for missing power and tuning.