Why don't you bump that Evi/Johnson 9.9 to a 15 HP, will need : 15 HP reeed valve assembly, carb and VA gaskets to have have factory converted 15 HP. Before you guys play with prop pitches must know wot rpm numbers with an induction tach, not blindy, as this could over rev or lug engine which is bad music.
Parts may still be available, will have better thrust, hole shot with a 15 than with a 9.9.
Is a T30 a 320 Mt sib ? if so, too much hull drag to overcome fast along weight with a poor 9.9 HP engine.