Sorry to perhaps not get the gist of your question.
I have several RM Young units and they either send down 3 AC pulses per propeller revolution or a current loop 4-20 ma depending upon wind speed, or a voltage (0-1 or 0-5 volts).
It is my understanding that the Davis system also uses pulses to indicate rotation of the wind cups, but more of a make/break square wave type of signal, and not a sine wave from the induced current in the coil was the Young propeller spins.
The conversion unit 6336 you mention I gather is now discontinued, but Miraculon has a unit in operation, and reportedly happily so, for many years. It also takes a company called NRS or some such, and converts it too.
There is no current option that I"m aware of to do that, so I think you'll need to do a bit of hardware or Rasp Pi work to take the variable voltage pulses, coming from the Young, and do some sort of detection that a pulse has occurred, and not being an analogue guy, I can't tell you what for sure to look for, but it will be 3 pulses per revolution. RM Young data sheets tell you a formula for converting revolutions per mph or knots or meters/second. Then you'd need to see what voltage levels and transition types that your Davis expects. I assume it was like the output from a Hall device, which I'd think, note my previous analogue inexperience, would be easily enough to produce with a transistor and pull up/down resistor. A friend of mine who lives, breaths and sleeps with this said it should be easier to do than I think, but over coffee he sketching something literally on a napkin and then never gave it to me, and i failed to follow up to have him do a bit more robust pattern for me.
If I vaguely recall there was a subject line somewhere that a fellow was trying to develop such a thing, and vaguely recall some DIP type of units of old op amps and then squaring circuit, and then voltage conversion, but can't find those old notes. As an aside, there was also a bit a few years ago about making something like a Davis head send info to older Heathkit ID-4001 and 5001 units, so there are clever people out there.
I wish I could provide more direct links, but maybe my bad cold induced ramblings will have other members recall some details or have tags on where to look for this.
I, like you, would like to have some sort of conversion board and the smarts to make it work well without false signals triggering it (try sending 20 word per minute CW ham Morse Code to see if it causes and error...)
Dale