I have the Tohatsu 9.8 long shaft (MFS 9.8A3 w/ electric start on my 74 C-22. Nice little motor but there's a few things you should be aware of.
1) I use a lawn tractor battery for starting (230 CCA). No problems keeping it charged. (Separate house battery... shore charged) We only motor about 1/4 mile from our berth to the end of the channel, maybe a bit further coming back in and the battery always keeps a full charge. It's three years old now. I love the electric start. I have a rotator cuff injury and I never have to worry about aggravating it or leaning over the rail.
2) Always run fresh ethanol free fuel. Religiously. With Sta-bil and Seafoam. Run the carb out of gas after every sail, even if your going back out on a few days. The carb is very sensitive to dirt. A dirty carb is NOT covered under warranty. I've been around carburetors since 1965 and after three cleanings I gave up and bought a new one. (Dealer wanted $150 to clean it, new carb was $169....)
3) Don't use synthetic oil, it will never break in. (Don't ask me how I know that). Keep your oil exactly between the high/low marks. If it gets too high it will froth up and you'll loose oil pressure. Since our running time is so short, my motor has the nasty habit of "making oil" caused by a combination of fuel blow by (see above...synthetic oil) and condensation. When it gets above the full mark, I siphon out as much as I can and replace it with fresh oil.
4) I replaced my motor mount with one that can handle the weight of the new motor. I mounted it at the same location and am glad I got the long shaft. Fully lowered, the tiller handle just clears the edge of the transom when it's horizontal. In a moderate chop (Lake Erie) the prop can come out of the water when turning or if a following sea lifts the stern.
Not withstanding my self inflicted problems with carb and the oil, it's been a pretty good little motor. Starts easy, plenty of power to push a C22, I can make 5-6 knots at 1/2 to 3/4 throttle in calm water. Past 3/4 throttle, the boat doesn't go any faster, the motor just makes more noise. There's no weight difference between the 8 hp and the 9.8 hp, only about $300. From what I've been told, the only difference between the two is a larger carburetor on the 9.8. We sailed at least 3 - 4 times a week last season and used only about 6 gallons of fuel.
If I had to do it again, I'd buy the 8 hp just to save $300, but am not sure whether the power tilt would be worth the $ or the extra pounds. I wouldn't use synthetic oil and would pay more attention to what goes in the gas tank.
Tom G