Bassclar, since my last post, I checked into this --- this thread renewed my interest in converting my clarinet... My original information was from a repairman, though I don't know that he ever made a conversion --- he may have simply seen the keys in the Selmer parts catalog, which of course dates the information (when did Selmer last publish a parts catalog??). I asked another repairman about it, who did a little research. Upon further investigation, it appears that the plateau keys in the Selmer parts catalog were replacement keys for a factory plateau Bundy, not conversion keys for a standard clarinet. He checked in some repair forums, and this seems reasonable, especially considering that a number of people have mentioned factory-made plateau Bundys.
Now, I do know a gentleman who *has* done custom conversions to plateau keys, and currently plays on a custom plateau Buffet.... I don't recall if *every* key has been converted (for example, LH3), but I know that he designed the modifications to work for him (he suffers from arthritis).
Sorry for any misinformation --- at the time of writing I certainly thought it to be valid. Thanks for the follow-up post.
By the way, within the past couple weeks there was a metal plateau Noblet on eBay..... Couldn't justify the cash outlay at the time.... Drat!
-DH