The gear highest up in the sequence will be linked directly to the spindle and probably rotate at the same 1:1 ratio with the spindle (check this). We can call it the spindle gear as if it were directly on there. The bottom gear should be the input to the gearbox
The gears are at a random position at the moment if I am getting the picture rotated right in my head. The 63 appears to be on the input to the gearbox ie a driven gear. It is never required in this position.
Imperial. The plate by the top left lever says eg "60,40,INT" and "40, 40, INT" the INT stands for "intermediate" and is just to bridge the gap between the other two gears so it will not change the ratio and can be any gear that fits.
The middle top plate shows you the threads you will get eg for third column 8,9,10,11,12,13,14 for each lever number setting BUT only if you have 40: INT 40 on the gears.
For the moment you are gong to have to put 40 on the 'spindle' and 60 on the gearbox with whatever fits, probably your 42 in the middle to bridge the gap.