i have a 1985 Baja 220 sport with a new 462 chevy big block roller motor alpha lower unit 21 pitch prop with top end speed of 60 mph at 4500 rpm I would like to get closer to 70 mph any ideas. With existing equipment or with a few changes

BOOST would be your answer.

one would think a big block would get that boat to 70. but 462 tells us nothing about the engine. it could be a round port head and truck cam engine and barely make 300 hp. or it could be something in the 500 hp range, but unlikely. first make sure your ignition is right and timing is correct. 2 or 3 degrees too low on total timing is a LOT of power left on the table. then make sure carb is big enough and jetted correctly. a 600 holley wont do it. so, tell us a little more about your engine. heads, valve train, comp ratio, cam, intake, forged or cast internals, ign, carb, exhaust. now, that being said, that 220 sport is a rather flat bottomed boat and will get skittish at speed. should be a fast hull, but is a flat water boat. and that alpha drive doesn't like power. it is a small light boat so that drive has a chance of surviving, but be nice to it from idle to 4000 rpm. that is where torque can snap that vertical shaft.