I was not eligible for the specialized coverage such as the Hagerty insurance above either. So, I opted to add my GT6 to my current Allstate policy with comprehensive and collision coverage, same as my late-model cars.
Sadly, if I sustain a covered loss to the 34 year old GT6, I won't get very much, maybe $3,000 maximum. Allsnake will settle the claim at "actual cash value" (ACV), which in insurance jargon means a depreciated settlement.
I know this isn't much help for an expensive car like a Healy, but it's better than no physical damage coverage at all!
Call your Agent and discuss, maybe he/she can help. If not, maybe you could use a new Agent?