OK, time to bring this thread full circle...
After mulling it over, this spring we decided to bite the bullet and go with a custom RH roller cam. We freshened up the heads as well, with new Ferrea valves (SS intake, their version of inconel on the exhaust). Cam specs are on the order of .604, both I/E. With our high-ish (cam builder came up with ~10.4:1) compression, he erred on the side of a larger cam, in hopes that the longer duration would keep cylinder pressures down. Something to consider on a marine engine that is always under load, he explained (this guy does solely marine engines). HP is estimated to be in the ~480hp range.
Got it all buttoned back up last week with new custom Manton pushrods, and it we did final assembly this weekend. We still need to play with props a bit (we're not hooking up great with the 3-blade 13x14), but it pulls strong all the way to 5700rpm and just over 62mph on the GPS (best of 62.8mph thus far). It pulls a decent number of guys out of the water pretty strong too- so it will serve its purpose. Feeling pretty good about having it back in the water at this point!