A 2 stroke will be lighter than a 4 stroke of the same size, which could be an issue with a fiberglass drifter. Make sure your transom can hold the weight of the motor before committing to it (shouldn't be an issue, but double check for sure).
With a drift boat, there's not a lot of point to putting a lot of horsepower on them. The hulls simply aren't meant for speed, and won't take much HP to hit your useful limit. You quickly hit a point where you don't get any appreciable gain by going to a higher HP motor, but you wind up burning more fuel and adding more weight than necessary. You'll probably be A-OK with a 9.9hp motor. I know it's probably not an issue - but with a 9.9 you won't need to get a boater's ed card for Oregon either (need boater's ed for any powerboat 10hp or over, hence the popularity of the 9.9). It's not a bad thing to get, but it's not needed legally if you stay below 10.