Well when all else fails, contact your insurance company, or any others that will be willing to speak to you, and find out how much they would insure a vehicle just like yours for. They might tell you something like, "we don't care what work you have put into it, as far as we are concerned it's worth $2K" or they might tell you that whatever the purchase price is plus receipts, or something like that.
I don't know if collector car insurance companies insure American iron, but they might, you could check with one of those. They are very very understanding when it comes to such things. I have had lots of luck with J.C. Taylor insuring a European car I own, I just declared a value and they had no problem with that. In the past I had a 68 Chevelle insured by State Farm and they took my word for it (I even offered to fax the bill of sale and receipts from restoration; they said not to worry about it). Hagerty has a good reputation among an owners' club I used to belong to as well.
At the worst you would get a polite "no," at the best a very helpful person who could give you a range of values that their customers have similar vehicles insured for.
