Bozak concert grand speakers

Have you tried to move them yet? They were designed with empty chambers intended to be filled with sand!

Oh no!  They have not been moved since installation in the 70s.  

Bozak Concert Grands certainly were NOT designed to be filled with sand.  I sold Bozak Concert Grand speakers back in the 70's and also have been to the Bozak factory that was on Connecticut Ave in South Norwalk, Connecticut.  Rudy Bozak showed me around the factory and I saw Concert Grands in the making.  I also saw how they made all their own raw drivers.  I repeat, they were NOT designed to be filled with sand.  The inside of the enclosures were pretty empty other than a thick type of insulation lining the interior of the boxes.

It sounds like you are not going to keep and use them, so is the question how to sell them?
They are a classic, though it would appeal to a narrower market due to size, weight and vintage. I gather that the crossovers could be improved (there was a fellow named Tobin, now passed, whose name came up frequently as the "Bozak guy"). 
You might get some traction (more Bozak enthusiasts) on some user boards with a Bozak group- e.g. Yahoo and Audio Asylum.
I don't think there are that many of these around, certainly in unmolested condition, given their price in the day, their size and the fact that your father's pair hasn't been moved since installation. I'd love to hear them! I know a guy in NY who was in a similar situation-- he hadn't set them up but was threatening to do that just at the time I moved away. Alas! :)
PS If you couldn't tell, I'm all in favor of your keeping them.