Do not, do not, do not put a turbocharger on a marine diesel, unless you need it for a powerboat or something. Weight is a secondary consideration for a sailboat motor, and you do not need a turbo on there. They rev like crazy and are expensive when they blow.
Moving up from 54 to 75 hp is a heck of an upgrade. What prop? What gearing? Can the prop take it the extra power? Does it mean a big three blade that you have to drag around with you when you sail?