League of Legends (LoL) Question: Tear of the goddess

I remembered that these things worked in some blizzcrank runes that I used but I think that Bliz Eternal Shield no longer takes care of it.

Manamune and Archangel's Staff both have 500 mana, and both of them gain an additional 360 mana when stacked. Once they transform into Muramana and Seraph's Embrace, they give 500 + 360 = 860 mana in total (of course, Seraph's Embrace gives even more mana due to its empyrean passive, but that's not what the question was about).

So yes, Muramana and Seraph's Embrace keep the bonus mana. Therefore they end up giving you 860 mana in total (disregarding empyrean).