422 dyno fail

Interesting dyno numbers.
I am pretty sure what likely isn’t causing you an issue, not as sure what actually is the culprit.
It isn’t the headers , run the same ones on my car, been 10.77 already, hoping to go faster, at more weight than the OP
Likely isn’t the carb either ( assuming it’s operating as it’s supposed to) Holley would be my choice, but years ago I tested a slew of carbs on a 416, several from Pro systems Patrick was nice enough to let me try, and from a 750, 1000cfm 4150, 1025 Race Demon RS 4150, and ultimately an 1100 Dominator, the difference from top to bottom was a bit under a tenth and a half at the track( more like 12 or 13)..that was from Patrick’s 750 to the Dominator( pro systems) and Race demon, which were virtually the same.
Carb certainly isn’t “Killing” this combo.
I doubt the Offy intake is killing it either. I ran a small port Weiand excellerator on my Eddie headed 418 that I just took off, optimal, no, but capable of way more than 100 horsepower above the OP’s dyno pull, and backed up on several combo’s at the track.
The head porting numbers and quality would be a good thing to verify.
Heads I just removed peaked at 270 ish at 550 lift, again, 10.70’s at 3300+
If the OP’s J heads are anywhere close to what he has been told, the motor is capable of making a true 500 horsepower, and potentially running real good in the 1/8 before wheezing badly in the 1/4… Those heads really will make the car a tractor.

To me, the cam is ultra suspect. I won’t run anything smaller than 260@50 on a 4 inch motor. 240 hyd roller is a very bad selection and is killing power. I would bet on it.
I also don’t like leaving compression on the table. Bumping up compression and camshaft would be the two things I would do with this combo before I started swapping bolt on parts on an off

to give you an idea, I had a bone stock 360 shortblock with stock Eddie’s on it that ran 12.23. Not sure what compression, but likely around 9 to 1
Mild porting of heads, and milled them to 61cc, ran 028 gasket on them, ditched the 240ish@ 50 Comp solid cam for the 260@50 Howard’s cam, and took off the missmatched( for this combo) Mopar M1 single plane, and swapped to an air gap.
No other changes, car went from 12.23 to as quick as 11.26 and almost 10 mph( more typically 11.40’s)
I attribute the gain to mainly the cam and compression, the guy did very little( as I found out later) to the heads

1. Cam
2. Compression
3. Are heads truly as nice as you were told/ airgap intake