In that case you can get a 5.2L Magnum and do the same mods, it'll make basically the same power but higher in the rev range. I do know the Magnum valvetrain (and hydraulic roller in general) is limited to about 6400 RPM. There were a lot more 5.2s than 5.9s made and the demand is much lower for them so it would be cheaper and easier to find one.