Hagerty and the other vehicle valuation references are not representative of the general market. Those sites utilize data from public sales, only.
Examples: Auctions, eBay sales, etc. At best, a very limited reference database. None of those sites have access to State DOT data or private sales.
Best bet:
List the vehicle on one or more of the reputable classic vehicle websites. Respondent offers will vary dramatically. In general, the 'low ball' offers will identify the resale ('flip') candidates. Obviously, your interest will be the parties that have personal regard for owning that specific vehicle.
Personal experience: Competitive negotiation will work to your favor
Good Luck!