Upgrading to push pull config?

It's hard to tell from the Asetek website.

If you look at your 510lc radiator you should be able to tell if you can attach a fan to BOTH sides. And your last fan would need to have mounting holes for the fan and the case.
The biggest challenge might be getting the right mounting hardware/screws.

I follow a simple rule when building a computer.
"If it looks like it fits, it probably does."

I can tell that you can put another 120mm fan on the other side, make sure you get the air flow the right way around. if you have then both pulling air from the rad you could damage the CPU with insufficient cooling.

If it doesn't quite fit, make it fit.  

+1 to that bro ^^

What kind of case do you have?
There might be better options for extra GPU cooling than depending on the Asetek 510lc dual fan configuration.

@Joedastudd and frombehind,

you obviously went to the school of Moto, well done guys  

@Op, it will be simple to do, just ensure your fans have screwholes both sides,
screw both fans to the rad blowing the same way (Exhaust I believe you said)
then put the assembly to the rear mounting place on the case,
feed a screw through the rear of the case into the fan housing, repeat and tighten once you can let go of the assembly
remember to plug the pump/fans in
job done hehe
just to confirm, asustek website shows a fan screwed to the case, then the rad, you can clearly see the screwholes on the inside, so you know they are in fact there, I think they probably allowed for the fact people would go pushpull when designing them, third pic on top row,
http://www.asetek.com/products/oem-standard-products/cp...
Moto

Thanks for all the helpbguys, for those of you wonering, Ive got a Raidmax Blackstorm case. Would I need to replace the existing fan as well?

It would be easier for you to buy two matching fans than just one that matched the original, which has obviously aged anyhow,
check the cooling fan roundup sticky at the top for some good fans  
Moto