An inspection of the instruction with a magnifier, indicates that the upper #53 flanged plate is located at the 14th hole from above, bolted directly onto the girders (5-hole spacement). This definitely only could work if the spacement at the base would be 9-holes. But the instruction shows an 11-holes one (red arrow)! So, I had to place the plate on the 16th hole from above (also shortening the outer stay two holes, blue arrow), and mount the plate on a #3 strip (green arrow). With everything in place, I then thigtened all the bolts.