New heads or repaired cracked heads will crack again unless something changes in the operation. Demand for more hp and a smaller footprint has diesel makers adding turbos to engines, some not really designed for it. Adding a turbo & intercooler doubled the hp on 6v53 from the natural 210 hp. If you run wot and have pyrometers, you're probably exceeding recommended EGT. A 4 valve engine has all that combustion heat confined to a really small area and only
coolant can absorb it. Maybe a bigger
water pump">raw
water pump from a bigger Detroit and a
coolant pump with more blades on the impeller would help. In
racing engines more flow is helpful and some reverse flow so the coolest coolant enters the
head first.
The only rating I have shows a max of 2800
rpm, but no continuous rating. The 2 are different, especially on turbo engines.