I ordered my 1987 25' watkins new with a 12 hp long shaft ob mounted on the transom. The transom does have a reinforcing backing plate. It worked fine even in 6' - 8' waves and the prop never broke the surface (1996 August off Cape Romano Shoal FL). I replaced it in 2000 with a Nissan 18 hp long shaft on the same adjustable mount. It workes fine. Steering with the spade rudder is better because there is no prop wash over the rudder surface. I have electric start, manual start backup and cockpit mounted controls, don't see how you could do otherwise on a 30 footer. A 9.9 is too small, 15 to 20 hp would be better. Manual adjustable mounts can accomodate up to 25 hp and hydraulic mounts that much or more. Fixed mount is ok as long as you can tilt up the shaft to get it out of the water for sailing and keeping the prop clean and avoiding electrolysis. Adjustable mount lets you lower the engine to maximum if needed in rough seas. 12 hp was 80 lbs and 18 hp is 100 lbs. NO significant difference in trim. Using up the water in my 40 gal tank under the v berth has more effect! However this is and Islander 30 SAILBOAT right? so you will only use the outboard for getting into and out of the marina anyway. I used the 12 hp to go 700 mi from Tarpon Springs FL to Savannah GA on the ICW sometimes inside sometimes outside. No problems except 2 spark plug changes leaning over the stern. Cost in 2000 for my 18 hp Nissan was $2,600, I installed myself.
2 cycle outboards over 40 hp are still legal to sell, the racing lobby saw to that. California could be none, not sure, don't boat there don't intend to.