I don't know the market price for this car even though I do have an appreciation for old cars.
In your original post OP you made a quick mention that your relative was having a difficult time finding a buyer, but the implication I got was that she just wasn't doing it right? Is that accurate?
Obviously a platform like BAT is a godsend to buyers and sellers alike and would be one such option, others have already been mentioned.
But I'm wondering if you really know the value ($30k, as you said). Did you do any real research? As I said, I don't, but in my opinion the market for this car is diminishing every day, unfortunately, as I think it's older gentleman that are most interested in this type of custom, and many that are interested would rather build their own (or rather have a shop build it for them) than buy one that someone else has modified to their own taste. What's popular right now is cars that show their age with "patina" and are mostly original. Of course there is a market for everything, but perhaps your relative has an inflated opinion of the value and that was the reason for the trouble selling?
This was a long way of saying, don't pay too much, or rather don't expect to get too much upon your own sale.
Good luck, looks like a fun car to drive, I would suggest a fake ZZ Top beard for the proper experience.