There are not alot of HEC power supplies here in the US or in Europe honestly so it's hard to find a real review of that model. I do know HEC makes all of Cougar's power supplies are they are mid range, not crap but not a high quality brand.
That model shows 648 watts on the combined 12v rails. Since volts x amps = watts we just divide 648/12 and get a true figure of 54 amps on the 12v rail. A system with a single GTX 670 needs a 30 amp 12v rail and adding a second card requires another 15 amps. Factor in some overclocking and you are looking at ~47-48 amps needed.
So assuming your power supply can actually supply the rated wattage and amps it should work. You are cutting it really close though. Personally I would feel better with a good ~62 amp 750w PSU. But it's up to you if you want to try it. In reality your cards will almost never pull full load. It all depends on the quality of your power supply.
Then i will go for it, whats the worst that can happen if there's no enough power, right? Its just trying to save 200 dollars
So thanks ^_^