Quote:

the car is drag only, i have 2"fenderwell headers hooker super comp

A 500+ CID engine will be restricted by the Hooker A-body 2" fenderwell headers. They are just way too long to make peak hp. With high stall and 500+ CID at 3000 lbs you don't benefit from the 4000 rpm torque they make.
Think about 2-1/8" (or stepped 2 to 2-1/8) that are only 30-34" long. Likely to get you 30hp peak improvement. And more if you RPM higher
Quote:

Fast68plymouth dyno test, 493 CID
Includes Hooker Super Comp A-body fenderwells (2" x 43")
versus his dyno headers, stepped 2 to 2-1/8", 32" long (12" + 20")

test A-M1 4150/905 carb/1" open spacer/dyno headers

test B-M1 4150/1050 carb/2" adapter/dyno headers

test C-M1 4500/1050 carb/no spacer/dyno headers

test D-M1 4500/1050 carb/no spacer/ A body 2" headers

rpm---A/tq/hp----B/tq/hp-----C/tq/hp----D/tq/hp
rpm--A/tq/hp-----B/tq/hp-----C/tq/hp----D/tq/hp
3700-----------------------------------------586/413
3800-----------------------------------------598/433
3900-----------------------------------------607/451
4000-521/397-----------------524/399---619/471 = +72 hp
4100-525/410---519/405----524/409---632/493
4200-555/444---533/426----545/436---631/505
4300-594/486---588/481----599/490---635/520
4400-605/507---594/498----617/517---636/532
4500-611/524---618/530----618/530---640/548 = +18 hp
4600-628/550---623/546----628/550---635/556
4700-632/565---634/567----630/564---635/568 = + 4 hp
4800-628/574---637/582----635/581---632/578 = - 3 hp
4900-630-587---632/589----634/592---626/584
5000-624/594---625/595----632/602---619/589 = -13 hp
5100-623/605---626/608----625/607---619/601
5200-617/611---622/616----624/618---612/606
5300-615/620---621/627----619/625---606/612
5400-609/626---620/637----609/626---599/616
5500-603/631---606/635----612/640---593/621 = -19 hp
5600-591/630---600/640----599/639---586/625
5700-587/637---600/651----597/648---578/627
5800-585/646---592/654----592/654---576/636
5900-578/649---589/661----584/656---560/629
6000-571/653---581/664----580/663---553/632 = -31 hp
6100-565/656---576/670----576/670---550/639
6200-557/658---567/669----560/661---538/635
6300-546/655---561/673----556/669---526/631
6400-541/660---549/669----544/663---516/629
6500-530/655---541/670----540/668---504/624 = -44 hp
6600-518/651---535/672----527/663---494/620 = -43 hp
6700-509/650---523/667----518/661---484/617 = -44 hp