Hello: I was unaware of that Mishnah Berurah. Rav Schachter always quotes that Chassam Sofer Lehalachah. We see that the Eivah exists and that it comes from the perception that Jews refuse to donate organs to save lives. Anything we can do to change that perception helps. Besides, if the Chareidi population of E”Y would be willing to be post-cardiac (and only post-cardiac) death organ donors then I guarantee you that the Israeli doctors would start using their organs. They have no other choice. So even if the Metzius in E”Y is as mentioned above, it could very easily be changed, especially if the Poskim would say that post-cardiac death harvesting is allowed.
And just as an amazing Mar’eh Makom, see the Ben Yehoyadah on Pesaching 49b, I think.