The LPG gas conversion your talking about seems to be more popular is the Netherlands and Australia than "here" in the US.
Having said that, while I'm here in the US, not this web site. Like all good things on the web this is an international resource. Somebody will notice your post eventually.
You may also want to ask the question on alt.auto.mercedes, and the list server at http://www.mercedes-veterans.com.
LPG conversions are being done in the US, but mostly at the fleet level.
PS. Leonidas rules!