Depressing Dyno results. Need advise

I have built 440,383,340, 318,360's...

Honestly the fuel line is fine those dyno guys don't really have a cluse, but they knew it was easiest to convince you that the fuel line was the problem.
dbl pump would be fine, if you can use your foot just right
I've put a 440 with 2'' primary headers, .530 hyd 286* 110* sp 830 annular holley double pumper, 5/16 fuel line stock fuel pump, nd it rev's fine to 7000rpm

I have pics of the car still and motor, it's a 68 dart.

either fix the timing, fatten the carb jetting and or have a look at the valve springs, cause they could be floating.

and try a different dyno shop, cause they aren't helping you by giving sht for advice.