Ken,
That's an interesting possibility. If anyone had some, I would think it would be them. I think the only things that would have been really classified back then would be the number, shape and position of antennas, and possibly the Fulton pickup system in the nose. However, the NVA and Viet Cong had an extensive spy network in South Viet Nam, even on our bases, and I'm sure if I went to a Hanoi museum, I could get detailed pictures and drawings .
Most of the ECM and sensor systems have been described extensively in accounts in books and online. In fact, I was startled at some of the information that has been released. But I guess that technology is old hat now and the principals are pretty well known. But I still don't talk about actual capabilities or characteristics. Just reading the details about new ECM systems in commercial magazines today makes me break out in a sweat when I think about the stuff we had to keep mum about back then.
Cheers,
Russ