I know your vortec heads will work fine at 5200 rpm,my friend runs them on his 20 ft. open bow v-hull.He's got a crower cam with .470 and .490 lift,otherwise stock except for holley 750 and aftermarket exhaust manifolds with transom exhaust. he runs high 60's at 5000rpm with a 23"laser.Does you boat have an alpha drive?I also run a 20'v-hull.Its a '92 350 mag.merc.Bravo one.I went the blower route first with a B&M 144,MSD ignition,750 Edelbrock marine,transom exhaust and holley fuel pump.With 4-5 lbs. boost it went from 58 mph to 70 mph. I just finished adding Dart 72 cc chamber heads to lower compression and a Crower cam with .553 lift with 1.6 roller rockers.I'm using a Merc. high five 25 pitch prop,which works the best out of all the props I've tried,might be the small diameter which allows more trim.The motor is going back in this week,I'll let you know how it runs! Regarding your boat,have you thought about a blower? Pacific Power Boats in Portland,OR.has a brand new B&M 250 for $1800 last time I checked.