Since things are a bit slow around here, I thought I'd share a little follow-up information about these.
The burners were made by A. and P. Gaudard in France in the 20th century, which (believe it or not) is still in business after some 300 years! Evidently the burners are 20th century, and they've been retrofitted into the older 19th century milk glass fonts and beehive candlesticks.
So what does this do for value? I don't know. I have to think that, since the burners are not original, it would bring it down a bit. I'm thinking maybe $300 for the pair?