Your “purchase and start serving food tommorow” theory is a recipe for failure, the first rule of taking over restaurants is to create your own Identity or you get lost in history and nostalgia or ad-nauseum discussions such as if Bryan and Amy were better than you as Ross Essner did.

At the very minimum you would have to change the name and gut/somewhat mordernize the interior to the tune of well over $1M.
Certainly old and new can co-exist if you see Ducasse’s Plaza Athenee restaurant or GILT at the Villard Mansion.

Assuming you even had the cash and were inclined to spend it, since it is as you describe it as a “Frank Furness mansion with Mercer-tiled fireplaces, leaded stained glass and walnut paneling”, you cannot even exhale in the building without calling the historical commission.

Trust me you would rather have a root canal without anaesthesia than renovate a historic building in Philadelphia.

Some rich dude should buy Deux Cheminees for his bored 2nd wife who wants to run the best bed and breakfast/Inn/microtel in town.
It would be perfect for that.
Seriously.