We called them fuel to noise converters.
There are some alluette II flying in switzerland. Verein für Exotic & Antique Flying Machines in Speck/Fehraltorf has one and Air Glaciers in Sion. Ask them what they think.
The Lama is more or less an alluette II with an alluette III dynamic system. A almost totaly different machine.
Parts are harder and harder to get.