Re: I/O to outboard conversion
You don't have to use a bracket either. You can rebuild the transom to the desired strength, and also build in some "knees", or braces from the transom the the stringers that supported the original drivetrain. This way it is bringing the weight closer to the boat, helping to maintain balance. One other thing to consider, weight placement in regards to balance is not an absolute. There are more than a few boat makers that have offered the same hull in I/O and outboard, without detriment to handling. The problem of weight distribution is fixed by moving the fuel tank forward towards the bow, under the floor, moving batteries, livewells if so equipped.
If it were me doing your project, I would not go back to I/O. You will want to go with a complete Mercruiser drivetrain, which people do not just give away. You will have to do transom modification as well as stringer modification to get it right. When all is said and done you will still have an I/O.
The question you have to ask is what is the intended use of the boat? Fishing, cruising? The next question you have to ask is are you so in love with this boat that you can't just sell it and find a boat that better suits your needs without all the hassle? You would save a bunch of money if you did just get another boat.
Now, if it must be this boat, then I will recommend an outboard conversion, without bracket, followed by a Mercruiser conversion. Costwise, its a wash, between a good, complete Mercruiser drivetrain and a good used outboard of significant power output. Good luck either way...