Hi Chucky -Here is a list of all EA projects (I will have them somewhere!)- just ask
I uncovered reference to what I think might have been a valve based (!) 2-4 ch convertor in the August 1972 issue of Electronics Australia. The article was entitled "Economical Quadraphonic Adaptor". I've only been able to find the contents page-
Would love to see it if you have a copy of that issue. Cheers!