We have a 1920’s Tudor with the old style single pane steel swing out windows.   These are face mounted with 6 to 10 inch deep oak trim on the inside.   My wife has finally accepted the energy increases.   None of the major window manufacturers  seem able to provide thermopane   face mounting but want to sell with a full return which would result in removing the oak casements.  Anyone know some flexible manufacturers or have any suggestions?   Still want to retain the Tudor appearance in the windows.