The drawing shows a few strange details. The position of the left diagonal bracing in the upper girder is 8 holes from end (blue arrow), while the right one is 7 holes from end (red arrow). Further, the height of the frame is supposed to be 10 holes (green arrow). This geometry doesn´t work fine, so that I placed both bracings 7 holes from end, and made the frame 11 holes high, which works nicely. For the mounting of the pivoting axle I used two #10 fishplates.