The reality is that OP has a niche product that has $1800 worth of tubes in its belly. Setting up a 400PS is also a bit of a black art; add more $$ for a competent tech who can ensure that you're not going to imediately smoke these vintage tubes in an attempt to turn a "divine gift" into cash. All assuming that there's nothing wrong with the unit in the first place that brought it to the eWaste pile.Looking at Reverb sold listings, they’ve moved from $800 to just under $4000, so it’s just a matter of patience and if it’s worth putting in the money to restore it, whatever that would come to, against potential gain.
I'd look at two extreme scenarios.
(1). You invest time, energy, and significant $$ into getting the amp professionally checked and tuned up, then try to sell a specialized product as a seller with zero history. Investment = big, return = questionable, if any. You have a downside risk of losing money as a bench charge+parts if it's not fixable.
(2). You take no action and sell "as is" without putting a dime into it. When selling, be honest with what you know, how you found it, and emphasize that it's a big question mark for the next owner. Investment = zero, return = all profit. While your upside will not be as large as the best-case if you'd refurbished a unit that needed nothing but a cleaning, there is no down-side.
There ain't no such thing as a free lunch. Even #2 requires that you photograph, list, and then pack and ship a beastly, fragile amp.
Consider what happens when "providence" meets greed.
