Mans,
I'm still a learner with an 'L' plate

. Having seen your pieces, I tend to agree with your opinion on the similarities with your Megantara. My comparison was based on the megantara piece featured in Ensiklopedi Keris. I presumed that megantara is associated with a luk 7. However, as mentioned by your goodself it may vary (based on your earlier post).
I've looked through Ensiklopedi Keris, Tammens vol.2, 3 and some other keris books and still cannot find any resemblance to the elusive 'c' shape.
BlueErf, I guess it's something exotic and unique to your piece.
Have you asked Dave, Paul or Adni's opinion? They should be able to assist...
Good day.