Hey!
I have a 1985 Horizon 170. I restored it a couple of years ago and I love the boat. I also have the 470 in it and with a little TLC it is a great engine. It is powerful enough to run the boat at 45mph and is pretty good on fuel. I even have the original charging system intact on it (most recommend an alternator kit).
If you have the 470, you really need to join the forum:
http://www.breezeworks.net/cgi-bin/MBoa ... readPage=1 since it is full of very knowledgeable engine folks for that engine.
I went out last Friday with family in town (6 of us) and the boat performed flawlessly. We went about 30 miles in the Detroit River area and had a great time.