If you go to our Pick-A-Kit helper at
http://www.caswellplating.com/pickakit/, there's a link at the bottom that gives properties for all metals. These should help you decide what's what.
The troublesome metals (require extra work and supplies) are pot metal/zinc die cast and aluminum.
Some of those parts are probably aluminum, like the brackets etc. and others are probably steel (like the bolts).
An easy way to plate all of these is with some Zincate (to prep aluminum) and a Flash Copper Kit (to plate onto pretty much everything including pot metal, steel and zincated aluminum). Once you've Flash Coppered, you can plate with anything else we sell.