Upon looking at the seller's feedback, it is interesting to note that they sold an almost identical auction back in December. The accompanying photos for the earlier auction look even more like a M.U.S.C.L.E./Kinkeshi mash-up than the current one:
At least the buyer appears to be happy with the purchase:
I also messaged the seller as I was curious to see their response:
It doesn't look like this seller is trying to scam anyone. I think our brief exchange inspired them to compare the material of both pieces more closely, and the conclusion they reached was that this in fact a Kinkeshi and not a M.U.S.C.L.E., which would make more sense coming from a seller in Japan.
The response of "old Japan rubber" would also seem to confirm that this is indeed not a Mag11-type situation. No M.U.S.C.L.E. SC has ever been found with the second piece, not even with those found still in the packaging.
Those pics, though, still look like an east/west mash-up to me. Especially the December pics.