This page outlines one possible way to fit the cheiroballistra little ladder tenons to the field-frame pi-brackets. The assumption is that the little ladder metal parts are made as described here. As discussed in the cheiroballistra article, it's impossible to push the little ladder tenons directly to pi-brackets outside the field-frames, as they're too close to each other. This article shows one way to work around this. From practical standpoint, it'd make a lot more sense to make the cross-pieces and rungs wider from the beginning and skip all this bending nonsense. Unfortunately, this means changing the numerals in the text, which should be avoided unless absolutely necessary.
The process step-by-step Edit
The first thing we notice is that the little ladder tenons are too close to each other, if we've followed the manuscript text closely:
To fix this, we need to bend the little ladder beams outwards. Unfortunately the bends have to be fairly accurate, so making a wooden bending block helps a lot. Start by marking the outline of the block on a piece of wood:
Saw the block into the correct shape. Then drill a hole to it's wider end to accommodate the end of a clamp:
Squeeze the little ladder into a vise so that the little ladder rung's outer edge is in line with the jaws of the vise. Next bend the little boards carefully outwards until the wooden bending block fits in between them. After this clamp the wooden block to the little ladder run to prevent it from slipping:
Finally bend the ends of the little ladder boards inwards, so that they're parallel to the center of the boards. Adjust the bend and file the tenons until they fit snugly into the field-frame pi-brackets: