1st: where did you get those struts ?
2nd: white metal is soft, not like lead, but soft, not to porous.
3rd: yes it can be polished. I use 600 grit sanding paper, then 1200 grit, and finish with a "polisher" ( don't know the english word for it ) in my proxon motor tool.
4th: I allways use a primer on metal parts. First I clean the parts for any release agent, and then I aply a metal primer, I use a primer from my work, Im an aircraft mechanic so its an aircraft metal primer, I don't think its available in shops, I just use it because its free.
hope this helps.