The "housings" are made from metal to help dissipating heat.I assumed they would have the black plastic housing like the ones already installed [...] So did I order/get the wrong ones or am I really missing something here??
Apple required modules that went into the MacPro to have bigger heatsinks, as FB-DIMMs are real power hogs and produce a lot of heat (and probably the cooling system in those Mac Pro's is designed for the bigger heatsinks).
In theory you should be able to use the modules you received (the memory chips used could well be using a lot less energy and thus produce less heat than the chips from 2006). If the heatsinks on the new modules are not sufficient, you can see that in a temperature monitor with temperatures rising significantly beyond those of the original modules. You may also note higher fan speeds and - in the worst case - your computer crashing under heavy load.
If you want to be completely safe, try to return those modules and get some with bigger heatsinks.
You could also install them, run a long load test and see how memory temperatures develop.
It's probably difficult to find out more details about the memory chips used on those modules without installing them, as removing the heatsink can damage the module and thus voids warranty. Maybe there is some software reading the information once you installed the modules, so you can look up things like heat dissipation and power consumption.
But i don't know whether you may have troubles to return the modules once you opened the case and installed them, so if you want to be safe, give them back directly...
