Just FYI, I have seen the original dyno sheets from some of the F5000 engines around 1970 and they were WELL over 500hp. One Plymouth in particular was near 600. Fragile, yes. The top teams brought many sets of heads to each event and changed them nearly every session. I think lots of people said "oh, it's about 450hp" because it made the driver appear to be the the key component in winning
Heck my car still has the original Hurst Airhart brakes. Last thing I need is more power!