Interesting timing! I finally obtained a sealed copy of Akira Ifukube Works for Piano, Volume 2 (ZMM1011), released in 2010. It includes the two piano version of the complete score for the ballet “Fire of Prometheus” (1950) and the piano reduction of “Ritmica Ostinata”. The former actually exists in two versions. One is the original orchestral version and the aforementioned two piano version Ifukube arranged for touring purposes.
Coincidentally, I was listening to the two piano reduction of “Ritmica Ostinata” last night.