Diesel vs 4 stroke outboard???
If the boat has not been designed to support an inboard, you may put in about $7000 to redesign the hull and install stringers. Plus it probably won''t sail worth a crap. Might be cheaper on that size boat if you want inboard to just buy another boat with inboard. BTW...
a few years ago a Japanese man crossed the pacific with a Tohatsu powered launch. Treated properly the outboard will give you many years of service.