[pelican]

here's my 2 cents:

5.7 merc,MPI motor - put the correct prop under the hull.FORGET THAT SPEED !!! you want speed ? buy a contender/regulator/yellowfin...you have an inboard powered boat,not a twin outboard powered rig.
attempting to raise your cruise speed by upping prop pitch/diameter isn't the way to go.
ride of the hull suffers - time to plane suffers,and you're killing the motor,along with killing efficiency of the motor - you're sucking fuel like a jet...
running a gas motor,that's overloaded is kinda like holding your feet to the fire...the motor is overloaded,you need to open the throttle further,to get rpms - this causes the exhaust temp to rise - leading to lots of potential problems: detonation,valve failure,etc...all of which spells disaster for the motor....

diesel sounds good - but in a smaller hull like your's,it's not cost effective to spend that kind of money on diesel.stick with gas,gas motors when set up correctly,are incredibly efficient and reliable
little more to it than just dropping a diesel in - you're gonna need to modify the exhaust,bigger diameter is needed.you're gonna need to add return line fittings to the fuel tanks - this could turn into a big pain in the butt - you've got wiring,batteries - lots more to it than meets the eye

i'm not a huge fan of the stroker motors - seen quite a few problems internally with those...
i'm also not a fan of "reman" or "long blocks" - I like NEW,as in NEW,complete motors


speed:

everyone is obsessed with speed :

truth is,20/22kts in normal conditions is a good speed - you're not beating up the boat,killing the motor and beating up yourself.the 23 center console inboards,these ride the best !

speed costs money - increasing speed requires increasing both hp and torque ... there's a huge difference between that old 270 crusader and a new MPI motor...I believe you'd be very happy with a new MPI 5.7,propped correctly...