Legally Register Any Car

You need a valuation as well. Thanks to Kelly Blue Book changing their valuation tool, any car I'd want is way overvalued, and I'd pay more than I want on tax of the claimed value. (They use auctions to come up with a price, and those numbers may not accurately reflect a project car's value) They won't just take your word for what you paid, you need a baseline. That's my main hangup. But other than that, I think, that's all you need.
It's against the law to charge you more tax than you have paid. Stick to your guns, ask for a supervisor then call your congressman if all else fails. If nothing works lets get all old car asses together and change the laws!