Mordechai Günzburg, A.B.D. Brisk - Is there a source for the death date of Mordechai Günzburg, A.B.D. Brisk

in Hebrewbooks there is a book about the Gunzburg family. Did you look there? I emailed it to you.

On page 20 at the bottom it says as follows:
in the same generation and their family members of R' Naftali Hertz and R' Aaron and R' Shimon (Generation 8) we find:
a) the R"R Meshulam Olma Ginzgurg who "sat" (lived) in the city of Wien and died earlier in the year Tet Zain (1656)
b) the Genius R"R Mordechai Ginzburg son of Benjamin Wolf who was AB"D of the Brisk community from the year Taf Lamed (1670) till his death in the year Taf Mem Chet (1688) (later in page 21 it mentions he was also from the deportees of Wien.
there is a source for Mordechai Ginzburg - (7) which says : Tzemach David, and look at Ir Tehila (warsaw 1886) side 27.