This is one area where I can offer help. I work in the auto insurance industry, and in fact my previous job was with Great American Insurance. I work in the claims department, and am a licensed appraiser, so I've got plenty of experience with this stuff.
If you insure the car with State Farm, Allstate, etc...under a "standard" auto policy, like you would a Honda Accord, they will give you Actual Cash Value. Those numbers are determined by a number of different methods, depending on the insurance company and state laws. Some use NADA, RedBook or other paper guides. Some use services like CCC, which is a lot more detailed of an appraisal, as they look at local cars for sale, condition rating down to the tires, etc....but it is still ACV. Some standard lines insurance companies will write a normal policy like you'd have with the Accord, but give you an agreed value. That means that you and the insurance company agree that the car is worth xx,*** dollars and that is what you will get if it's totalled. That is different than a stated value policy. A stated value policy means that is what you are saying the car is worth, and you could get up to that much, but the insurance company has the right to make some changes depending on the condition of the car, etc...A stated value policy usually doesn't require an inspection, an agreed value policy might.
There are companies such as Hagerty, American Collectors, Great American that will write a specialty policy for these cars. They restrict you to 3,000 or 5,000 miles per year, but the premiums are much cheaper. They are usually agreed value policies, so there is no question of what you'll get. They also usually have no deductibles and great benefits. The trick to these policies is that they are restrictive. Many of them will not allow you to drive it too/from work, or other restrictions. You must abide by the terms, or the insurance company can and will deny your claim. They charge low premiums because they are believing the risk is very, very low since the cars will mostly be used for weekend cruises and such.
I will also say that contrary to popular belief, the insurance companies are NOT out to rip anyone off or pay them less than they owe. I'm a manager of a claims group, and I can assure you that we, and others in my position preach to our staffs to pay what we really owe. The insurance company will not try to undervalue your car so they can save money. They do the best they can to come up with a value on the car. The problem with cars like the Viper is that value is a very hard thing to determine. It's not like a Ford Taurus, where you can find 100 of them within 50 square miles and easily come up with a value.
If I can be of any help, please let me know.