I've seen similar results with similar parts more than once up
Dan,AKA Dram, (may he R.I.P.) didn't believe those results years ago shruggy
My first pump gas stroker 400 with 4.250 stroke and 4.375 bore with 9.25 to 1 compression ratio with a set of ported big valve iron 906 heads with a low deck six pack Eddy intake set up with OEM 440 six pack carbs modified by C&J engr..made 612 HP at 5500 RPM and 644 Ft. lbs. at 4500 RPM using CA 91 octane pump swill boogie
Your heads are probably better than my old ones were up
Be VERY careful with your new found power, it can bite you luck

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)