Opel Kadett C with LPG ?

Hello ! I have seen at E**Y a B-cadette, which is equipped with 1.1L engine (so carburetor) and an LPG system. Who can tell me where I can have such a thing done and what it costs ? I know this so far only for injections of the newer generation, like my own BMW, which has a gas system. But carburetor, oldtimer and LPG ? Please for your help and experiences !!