 Sterndrive/ inboard/outboard vs outboard
How about a little bit different perspective? I decided to do the same thing you are looking at two years ago. I knew for certain that I did not want an I/O because the boat would be in a slip and I don't want the maintenance hassles. So I thought that I would buy a quality older fish boat hull and repower with a new outboard. I was getting pretty discouraged after looking at a bunch of thrashed hulls and discovering that a buying a big new outboard requires a mortgage.
Then my wife pointed out an old 20' Shamrock that she liked because of the lines and the huge cockpit. I had never considered an inboard for fear of tearing up the running gear. But this boat had a full keel that protects the running gear from anything but a SERIOUS boat crushing accident. So after an internet crash course in inboard power via the excellent Shamrock owners board, I decided that it was worth a try.
So I ended up with a 1988 20' Shamrock inboard and now I am hooked. I found that I can actually deal with shallow water better than I did with outboards because the running gear is protected, it draws less than 2' and the water intake is not down in the muck. Fuel economy is excellent, parts come from NAPA, I can work on it without electronic gizmos (unless you count my timing light) and you don't lose fish on the engine or outdrive. Also, with the engine down low in the middle of the boat and that keel, it drifts and trolls better than any 20' boat that I have ever been on and better than many much bigger boats that I have fished. Plus the price seems pretty stable on 1980's Shamrocks so I might be able to get most of my initial investment back when we move up.
Drawbacks? It isn't as fast as outboards or I/O's in good conditions because it is dragging that keel around. But it is also better than most boats this size when things turn ugly because it is dragging that keel around. It is a wet boat so the curtains stay on board all year in case we need them for choppy water and wind. The submerged exhaust requires that you pay attention to the condition of your boat (not exactly a BAD idea on any boat though).
The boat was in excellent condition and cost about $10k. As far as refurbishing this boat over the last two years: $550 for new manifolds and risers; $100 new exhaust hose; $200 for a rebuilt carb; around $50 for a complete tune up; $100 to eliminate the points and condenser; and maybe $100 for all new raw water and fresh water hoses and clamps. In other words, a pretty nice fishing and cruising boat for less than the cost of a new outboard! | 
