They are the "same card." You can crossfire them. You'll probably have to put the single slot one in the first slot. This placement may be the only way they'll fit. If not, it doesn't matter which order you install them.
Yes you should be able to Crossfire those two cards. I would put the wider card (since it has more output choices) in the first slot (The long slot closest to the CPU). The other card goes in the other x16 slot (see your motherboard manual if you're not sure which one). Make sure you link up the two cards with a crossfire bridge. Hook your monitor(s) to the card in the first slot. Then boot-up and go to Catalyst Control Center and enable Crossfire. Update your drivers often and install the Catalyst Application Profiles.