I recommend a 17" setback. Moving the engine back off the transom affects the center of gravity of these boats. The further back the engine, the lower the stern will sit in the water. That is why most people try to shift some weight forward to compensate.
And the vertical lift for a 17" Porta bracket is 12". The vertical lift for the 21" setback is 15" (per the Porta bracket website).
And make sure you post some pics of your restoration -we love boat porn!