How well would 150mm x 50mm aluminium box section work to manufacture a WR650 waveguide for hydrogen line radio astronomy? What other commonly available sizes could be used to manufacture homemade WR650 waveguides?

Dimensions of WR650 waveguide for hydrogen. For the neutral hydrogen line at 1420.4058 MHz, WR-650 is the standard rectangular waveguide size most commonly used. Its dimensions are: Dimension Inches Millimetres…