Is this simply a display rack or do you intend to store your rifles on it? I store my rifles inverted, that is to say, muzzles down. Otherwise, over time, oil in the barrel migrates to the breech plug and causes two problems, ie: the oil turns to varnish sludge and interferes with ignition, and secondly, oil runs out of the vent into the wood around the breech and lock and ruins the wood. Just look at any old Winchester for evidence of this wood deterioration.
The rack in my lock-up has large notches cut into a 2 x 4 to support the butt stocks between the lock and the buttplate, and the muzzles rest on a 2 x 6 on the floor. There is no need to install dividers for the muzzles, though one certainly could.
Need a picture?