I am not really sure where you got the above information, but I was told by a couple of distributors (John of carolinasrc, and a tech from amain) as well as mugen that grp basically screwed them over. They created the Ninja and it turned out to be such a highly sought after product, they basically stopped producing it and concentrated on their own line. (changed the ninja name, rounded a couple numbers another way, changed the timing oh so slightly and BAM the new GRP) Even the pipes are the same (2053's)

One things for sure though, Mugen would not swap over to OS just because they wanted too.... they had too. Why on earth would you change manufacturers when the product was such a hit? (and less then a year after initial production no less) That would not look good on their company at all!