Third Holley they designated for the never-installed-at-the-factory cross-ram intake, 600CFM.
http://www.camaros.org/crossram.shtml
Camaro Cross-Ram Intake Manifolds
"By the summer of '68, these carbs were replaced again with a different pair of 600-cfm Holleys. These were LIST 4295, #3957859, ..."
One recently sold on ebay, winning bid $3550.
http://www.ebay.com/itm/68-69-CAMARO...VX9Uvy&vxp=mtr
Here is a pair refurbished, opening bid $7000, Buy-it-now $9800.
http://www.ebay.com/itm/1969-Camaro-...3D152268104789
So yes, looks like they have some value. Looks like your dad has a small gold mine there. Congrats!!!