Holmes 440,well part of one

[Lantz70]

So I got this old homes 440 boom that I have been planning on doing something with for a while.I got to looking at it and it has some rust issues at the bottom of the boom I am just not comfortable with,so I was looking at having a set of pole booms made.Does anyone know what size,grade of pipe was used on the 480,s....Also,,,what is the piece that is in the center and reinforces the boom called and can they still be ordered?