GH3 and IR
Somebody did a test in this forum recently, with a few µ4/3 camera. His findings were that the GH3 is the least sensitive (strong filter) and the E-M5 the most sensitive (weak filter).
This could be the reason why you're experiencing focus problems with your GH-3. I wouldn't sacrifice a GH3 or EM5 for IR conversion, but I am doing it with a G3.
My nickel, since the penny is being discontinued...