Normally what I did was putting all 4 stand-off to the engine and then place the stand-off with engine on the transparency A4 size, using marking color to draw the line of those 4 stand off and make the center line in vertical and horizontal direction. Use transparency as a template on the mounting box of the airplane. Don't forget to have the right thrust so the actual veritcal line must be offset for 5 mm approx.