Hello, Dan - and welcome to the Forum. Thanks for filling in your location.
Now that that's done, and now that you're posting -- now we can get down to brass knuckles - or whatever that phrase is. Your 400 cc bike would run in the 35-500 cc class -- so yes, you can run it out there in a class, not for "time only". The top speed isn't important to be in the class - so you can go have a ball and get timing slips to your heart's desire.
Don't forget, though, that you will be required to have certain equipment (safety items, for instance) that meets the requirements for the top speed record in your class. I haven't looked it up, but for instance, if the 500 cc class record is 175 - you'll need gear that meets the 175 requirements. Good thing you've got a rulebook on the way - it'll answer lots of questions for you. We'll do our best to answer the rest - and help you find some more queries.
And finally for this note -- too bad you didn't get active a year or more ago. That's when we were still racing at Maxton, NC -- only four or five hours east of you. Now you'll have to go northwest to Wilmington, Ohio. It still won't be a "deal breaker", I hope. Going to events is probably the best way to learn - learn equipment, learn techniques of building, and learning who the other racers are. Plan on going to Bonneville, even as a spectator, as soon as you can. Once you've done that -- you'll be hooked.
Best regards -