The final assembly process of the field-frame bars is fairly simple. First bend the little ladder beams outwards and through the pi-bracket, until the field-frame bars lock into the notches in the beam tenons:
Repeat the process for the other end of the little ladder.
Next insert small wooden shims between the outer sides of the tenons and the pi-brackets, followed by two wedges hammered in tight:
The wooden shims should slightly higher than the tenons, so that the wedges squeeze them tightly against the pi-brackets.
Once all of the little ladder tenons have been wedged in place, insert the little arch into the pi-brackets. You will probably have to bend the field-frames outwards slightly and then back in, until the pins in the little arch lock into the pi-brackets. Tighten the whole package with two wedges per pi-bracket: