Attached is a file that functions the same but has been cleaned up a bit with the params/actions renamed and all the actions other than the scales moved to the Width parameter. Here's the summary...
There is the main Length parameter with the stretch action to move the lower arc and 'Scale Bottom Arc' parameter and to stretch the two straight sides up or down.
Scale Bottom Arc and Scale Top Arc are both chained linear parameters with their respective basepoints at the center point of their respective arcs. They each have a scale action attached that scales the respective arcs. When the arc is scaled larger, the endpoints move out to the sides and move up or down toward the center of the block.
The remaining actions in the block are associated with the Width parameter and coordinated to activate the two chained scales and to stretch/move the straight sides so that they meet the ends of the arcs. The Width parameter has had its 'Base Location' changed in properties so that it is Midpoint instead of Startpoint. What this means is that any action of either grip results in the other end grip moving the same amount in the opposite direction so that the midpoint of the parameter remains constant. I also changed the 'Distance Minimum' to 1/256" as allowing that distance minimum to remain 0 would result in the block failing if the Width parameter was moved to 0 due to the fact that the chained scale actions don't like that...
The first action is 'Stretch Top Left Grip 90 Ang 0.5 Dist' which is associated with the left Width grip with the 90 degree angle offset so that movement to the left stretches the top line ends down and movement to the right stretches them up. 'Stretch Top Right Grip 270 Ang 0.5 Dist' does the same for the right grip but requires the angle offset of 270 because in this case movement to the right should stretch down and left should stretch up. Because both of those actions will be activated with any movement of either grip (midpoint base location moves both grips simultaneously) and both actions result in the same movement of linework, the distance multipliers need to be set to 0.5 instead of 1.
The next two actions 'Stretch Bottom Left...','Stretch...' do the same for the bottom ends of the lines.
The final two actions are moves and they respectively move the left line and the right line. Because there is only one move action attached to each of the lines and they move in the same direction as the respective grip movement, the distance multiplier remains 1 and the angle offset 0.
