Thanks for the tips. Yeah, the .25" for the sides was in case i wanted to tap a fitting and was free/available. Top and bottom piece .125".25 is nuts for end tanks. I typically use .090. the best kind of kill is Overkill lol.
Looking good. If you still need to weld to the cast section, cleaning up the surface with a carbide Burr bit, file, or mill really helps. In addition to the absorbed contaminates, the surface finish off raw cast doesn't easily allow for oxide removal and can cause subsurface porosity.