Chris Craft built thousands of inboard boats with straight exhaust and no mufflers. Mufflers were an option and CC made some small cast iron units that were laid down flat in the bilge, but quite honestly you won't need mufflers and noise won't be an issue. The helm is so far forward, and the transom so tall, and the fact that the pipes will be partially full of steam and water means the noise factor really is not all that pronounced. With the twin tips you'll have the classic CC sound, and when under way you won't really be hearing much of anything from them either. My 20-foot fiberglass Sea Skiff has the straight pipes and noise is absolutely not an issue. You will also have considerably less back pressure with the twin exhaust.
The sound will be more noticed outside the boat than inside. Here is a bit what you might expect, this is my 20-foot Skiff, and your boat will have a little longer exhaust pipes but a similar sound. Then if you think the noise is actually an issue after really experiencing it first hand, then you can slap on a couple rubber mufflers inline somewhere and be done with it, and still have less back pressure than the original installation.