I have 2 cornelius, and 2 Firestone Challenger VI's they are pretty much identical. The rubber handles are slightly different in shape. The corny handles are a little bit more angled and sharp, the firestone's are a bit rounder, but all in all they are the same.
When you get your kegs who knows what soda company had them, and how many times they changed hands. You migh get differnet poppet valves, some will have the 11/16 connects, and some will have the 7/8. Some will have straight diptubes, others will have curved.
What I am trying to say is that if you specify Firestone or Cornelius, your parts won't necessarily be Firestone on Firestone, or Cornelius on Cornelius.
Another bit of info is that some of the later model Firestone kegs have plastic gas in tubes, and they suck! I got my 2 Firestone kegs from kegconnection, and the plastic gas in tubes were all deformed and one of them broke during reassembly after clean up.
I found a source for the plastic gas in tubes, but it is just easier to buy a SS gas in tube, and drill out the post on the keg to fit it, this way you never have to worry about one of the plastic tubes taking a crap on you.
Or...you can just order corny kegs and not have to worry about it because they are all SS. YMMV.