That combo should run 7.2s or better with what you have, The .509 believe it or not will go 10s in an A body, i've witnessed it a few times over the years, Black plugs is not helping you, another thing is making shure that cam is degreed, PS cams have a bad tendensy of being way off, & & overlap on the .509 its very cridical its checked & advanced apon install, The .509 works "great" with fairly stock heads. Your MPH sucks for the ET, I ran the XE284H in a 451 with 9.73 compression, bone stock 906s @ 3200 lbs., 4400 PTC 9.5" & 4.10 gears, Swapmeet 750dp, M1 single & headers. This cam was a bit less then the .509, Was set-up at 105.5, I shifted at 5600 & car ran many 7.0s in the heat & mid 6.9s in the cool air with a best of 6.91 on a 1.51, MPH was 97-99. At 3300 that car should be running 7.2s @ 96-97 with ease IMO. So get to working the bugs out & leave the cam in, just degree it.
If your running basic FTs around .020" below deck & un-milled open chambered heads your not at a true 10.5.1 i ashure you.