I'd recommend you read your policy. I would guess that it probably covers this issue. I'm also going to go out on a limb here and guess that since the insurance company wrote the policy, it'll say they can use whatever parts they in their sole discretion deem fit to use. I hope I'm wrong!
One thing on this, when you say NOS, I picture in my head a part that has been in a box since the 60's. Some people say NOS and mean "Ford part". They really don't mean the same thing because Ford replacement parts may be completely different then the part that was originally used.
I guess if was an insurance company, I wouldn't spring for NOS unless somebody was paying me an outrageous rider that was covering my risk for that. And even that wouldn't cover the risk, because a lot of these parts aren't even available NOS. Heck, some aren't available NOS, replacement, or reproduction, and that's with mustangs. Imagine if you needed some darn trim piece for a 1965 Falcon Station Wagon! I mean, let's say there are only one or two in existence. Is the insurance company on the hook to pay someone what they would charge for that? Let's say there aren't any in existance. Is the insurance company responsible to go somewhere and have someone tool up and make you one?
Read your policy. My guess is you'll find they've covered their tail 6 ways from Sunday. Then work with your body shop and let them know what your expectations are UP FRONT. Then make sure they meet your expectations.
GOOD LUCK!
Phil