Q. Ashkenazi bochur that davens in a Sepharadi shule; should he wear a tallis godol?

A. To follow the minhag hamakom, (the custom of the place,) is an accepted universal principle in Halacha. See Or Letzion (2: 2) in regards to a Sefaradi bochur learning in a Ashkenazi yeshiva, he rules that he should wear his tzitzis on the outside, as everyone else does. Se also a similar question in Toras Hayeshiva (p. 18).
Horav Shlomo Miller’s Shlit’a opinion is indeed to follow the minhag hamakom. However, he added, that if there is already a distinct and defined group of people not wearing a talis, he may join them.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a.