What motion limitation are you countering?
Among the booms that I use on location (no studio these days) is one feature that I was happy to see appear on the last two arms I bought: a casting on the end that allowed me to choose whether the 5/8 stud projected in the axis of the boom or stuck out at a 90-degree angle. That angle could be "up" or "down" or sideways. I have Einsteins and the swivel hinge fitting under the head only allows a certain amount of yaw back, so I always start with the stud pointing 90 degrees "up". (Is this clear? Hope so.)
You have identified two interesting pieces and I think $50 to buy (ship$) and perhaps you can skip that expense. That said I love having all these pieces in my rolling box for location, but these look optional. A piece of bar stock, a 5/8 socket, and a 5/8 stud, could stand in for the short arm.