I ran a BB with an older Gale Banks tiwn turbo set up. It worked great. Will fit under your engine cover. Gets way better gas milage then my 8-71 did. Uses a small cam with a good smooth idle. And best of all, it's not very loud. At mid throttle it was runnig under vacuum and a full throttle it made 12 psi. I ran pump gas and got away with it. If you can find a good used one go for it. But a new Race Arrow set-up might cost as much as you boat.
I can send you a pic of my GB set up if you would like.