I have done the floors casting platform the whole enchilada, I was body work and paint away from dropping the I/O in. Until I took the sawzall to it :-) I plan to cap the top of the transom off, heres what she looks like now
You can see I cut more toward the transom as I didn't want to screw myself trying to do something with the top cap to meet my new transom cap, I came back 16" from the transom which is where my new cap will be.