Rear drag shock settings
did you have your motor dynoed? I know you only have 3.55 gears, and full interior, but 500 hp would get you way more than a 7.90. thats assuming you hook well, and you said that it usually does.
anyway, my set up on my belvedere bracket car is identical to the settings that Flyfish had in his pic above. it usually pulls the tires almost as much as his, and has been 7.40's with those settings. with much less than 500hp.