I would put about 60% of the weight up front as much as possible, since it's an i/o. In an i/o you already have the engine weight in back, and you will need to put the trim up(about a 1/3) in order to clean up the wake. When you put the trim up, if you don't have weight in the front, then your boat will porpoise(bounce) out of control. So about the rest of the weight can be put in the middle/back. Also, you may want even more than 1200 lbs if you can.
I have an 18.5 ft i/o and put close to 2000#s, granted it barely moves, and sucks up gas, but the wake is alright..