I can see why Woodys getting frustrated. You're asking for answers, and then telling him he's wrong. If you try and put a steel lintel in, you may well need to take the window out first, support the upper courses with a strong boy, get the lintel in, and then reinstate 4 course. Now if you wedge the LH side up so that it can't drop, and then carefully take the dropped bricks out, then put in a (preferably a curved) former on the RH side, and then cement the bricks back in using bits of slate as you've got to really shove things together, then you should be fine. If it's not tight, then you may get a bit of dropping later, and have to repoint a couple of the courses above it at a later date.