A new organization, named St. Louis Junior, was composed entirely of mechanics, formerly connected with the Atlantic, Jr., and they located on the old Veto grounds, near the Pacific machine shops, with Joe Blong president.-E.H. Tobias, writing in The Sporting News, December 28, 1895
So according to Tobias, Blong is in St. Louis in 1871 playing baseball. We know that Blong was at Notre Dame in 1869 and I had guessed that he may have been there at the same time as Packy Dillon and Trick McSorley. However, it's known that Dillon and McSorley didn't enter Notre Dame until 1872.
Since the StL Juniors were "composed entirely of mechanics" and "formerly connected with the Atlantic, Jr.," it may be safe to assume that after leaving Notre Dame Blong was playing baseball with the Atlantic, Jr. and working as a mechanic in some capacity.