As far as the mystery chunks goes, I ended up liking the plain steel one the best. It was the only one besides the 18-8 stainless steel one that did not have markings on the top, which ascetically looks much better than the ones that had markings. Between the 18-8 and the plain steel ones I would say it depends. If you're building a newer looking saber, the 18-8 stainless ones look more futuristic and shiny new. Personally on my saber since i'm going for a more beat up look I prefer the plain steel which, is a darker and grittier texture. It looks blacker at first because it's covered in oil but if you wipe that oil off it looks lighter in color, which I find to look the most like the aluminum. Since the real piece that goes there is unknown but is said to be aluminum. I assume that if they used a similar screw or separate piece of metal the chances that it was stainless steel are rare ( In 1979 stainless steel was less common, correct?). So I figure that chances are that they used something made of either plain steel or aluminum.
Sorry, that was a little more long winded than I had originally intended it to be.