Henrik Krogius' recent history of the Brooklyn Heights Promenade has surfaced some great photos of the BQE. Both of these are attributed to Louis Casey. This one shows the old walls of Brooklyn Heights that would become part of the promenade.
The one below is dated circa 1949 in the Brooklyn Heights Press and Cobble Hill News story about the book but I have my doubts. The cars and vans zipping by on the eastbound BQE look more like 1960s models to me. Something about the kids' haircuts, too, is bringing back memories of the mop-topped mid-sixties.