One thing that the pair does not represent is, "It ain't over 'till the fat lady sings." Someone might think that this is the cliché represented here as a visual pun—with "over" understood in a particularly macabre sense—because the operatic duo really are near the end of the ride, but the "fat lady" phrase appears to be a recent coinage, not firmly attested earlier than the mid-1970's.
The phantoms of the opera went from Marc Davis's original sketch to maquettes to finished figures with less alteration than practically any other characters in the HM. Marc just flat-out nailed it, and no one could improve on it. It almost makes these characters boring to blog about. They sure are fun to look at, though.
*I can't find the attribution for this photo. If it's yours, contact me, and I'll give you full credit or take it down at your option.