Your question got me looking into the issue also. From everything I've ever read. The redline of an engine has to do mainly with valve float. On a hydraulic engine, I've seen lifters rated at everything from 5000-7000 RPM. Alot of that has to do with valve springs, push rod deflection, etc...
In my boats, I cruised at anywhere from 3800-4800 RPM all day long.
There's more to the redline issue than just valve float. Balance, oiling, cooling, bearings, and stroke all have a role in the entire scheme of things.
The 230/ 250 engines have a 3.25" stroke, they should be able to rev quick and have reasonable balance at higher RPMs. I'm willing to bet they could do somewhere north of 5000 without any il effects.
