Tom,
This is a barn find I stumbled across a few years ago
It was in exceptional company. The car on the left is a like new Allard and the Benz on the right is a 300 SL Gullwing. In total there were more than 30 cars in the 'barn'.
The plate the guys are talking about looks like this
My barn find Cobra needed to have the engine rebuilt - it had seized up! After the rebuild it sat for a while as potential buyers mulled it over in our bad economy. A sale is finally about close and the agreed upon price is middle six figures.
This should give you some sense of what yours is worth.
BTW if your cousin is really serious about her executrix responsibilities she will not get secretive about this stuff. The #1 responsibility of the executor / executrix of an estate is to be sure all the taxes are paid. In the event the estate has insufficient funds to pay the taxes she becomes personally liable!
It is decidedly in her best interests to get fair market value (or better if possible) for the estate property. A turtle/ostrich mentality is a sure way to get into trouble. Get some professional counsel and pay attention to what the guys on the site here tell you, we actually have some lawyers on here who are Cobra enthusiasts and they are pretty smart guys.
Ed