hey bob,retriever,that boat,it has straight inboards-i think you're looking at the rudders thinking they're outdrives-a blackfin like this one has outboard rudders...
You're right... I looked at the first photo and though they were MERC drives... Hey... black and stuck out the back!!! L.O.L.
Converting a straight inboard to O/B w/brackets is even crazier. Not only do you have the transom strength/support issue as you indicated, but you will totally louse up the trim of the boat.