Champion radiator - I cut her open

To clarify,
This rad was in the car before I rebuilt the motor. I had issues with it previously, so it was on my kill list.
Fresh motor build, About 500hp, tested the new tstat, plenty of airflow, timing 12/36, tried a bit more, no improvement, new rad cap tried a few . Even put a pusher fan on front and 2 pullers with a shroud, Still didnt cool her down at idle.
Cold to 220 in 15 mins at idle with fans on all the time and no hood on the car.... Wtf....
If I'm driving around, maybe I'd get 25mins of drive time before I freak out and it's up around 210.
Tried a few different radiator flushes, Pulled it out today and cut her open. Out of all those cores I had approx 12 cores partially blocked, Probably from before the engine was rebuilt.