With 2 engines with the exact same displacement, 4 Stroke will let you develop more low end torque but a 2 stroke will usually give you more power to turn larger propellers. That is why you will need a 90 2 stroke or a 120 4 stroke. (My preference is 2 stroke, sorry guys)

If you need the weight in the nose to get it to balance, then by all means, the 4 stroke is the best choice.

Last, is the tuning. Running a 2 or 4 stroke engine rich will cause a decrease in power and a mess on your hands. It is easier to distinguish a rich run 2 stroke than a rich run 4 stroke. When the engines are run lean, the 2 cycle will generate a lot of heat and wear while the 4 stroke will begin to backfire and throw the propeller and spinner. Usually a lean run 4 stroke will not run very long.