Just saying, Indy and Koffels sell aftermarket blocks. The more people they convince that 600+ is unsafe the more blocks they sell. Some people have success above 700 HP and some do not. My 500 has many runs from 700 to 900 HP.
LOL you beat me to it. They do sell blocks, and good ones at that. If 600hp is a limit for a BBM, I guess I need to make a lot of calls to tell some of my customers that their engines I built many years ago are no good.
HP is not the limiting factor, its Harmonics, detonation, balance ect! Tame these, and you can make a ton of power without worry.