It's more of a matter of preference. You can mount the fans on the inner side to blow air through the radiator and out of the case.
You can mount them on the outer side to pull air through the radiator.
One main choice on this is whether you have enough room in the case to mount them on the outer side and still be able to fit the radiator.

Pulling air through will be a slightly different airflow because instead of pushing air through the one gap, the air is trying to be pulled from any available space, not just the fan centre.
Personally, I prefer them to pull air through the radiator.

You won't notice a temperature change using either method, if you do it will be minimal difference.

It does not matter which side you put it on, what matters more is if you want push or pull.

imo i would have it mounted out the outside pulling air into the case since its going to be mounted on the front.

New Problem ..

The wires for the Power button, front USB's at the top of the case are blocking the space for my Radiator to be installed. ive tried everything and there i literally no way it will fit in. the space is there but it cant reach the screws because the cables that are going to the Power button LED, front USB's & front audios etc are blocking itt..

+major rep too anyone who can help with this its really f*cking frustrating

Putting the fans on the outside should create some space.

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right.. back to unscrewing then again..

so doesnt this just suck air in but move all the hot air back into the machine?

DMstratz wrote right.. back to unscrewing then again..

so doesnt this just suck air in but move all the hot air back into the machine?

It depends which way you have the fans facing. not what side its on.

I would have it pulling fresh air in so that theres better airflow in the case.

If you have it pulling air out all you will be creating some negative pressure.

The fans should have little arrows on one of the sides. The arrows will point in the direction the fans will spin, as well as the direction the air will be going through the fans. Since you have to front mount the rad, you should have the fans pulling cold air in, through the radiator. You should have other fans in the rear and top of your case, pushing the hot air out. The S340 should come with a 120mm in the rear and in the top as stock, and the X61 comes with 2x140mm fans as stock so you'll be fine, you'll have more air coming in which means that any excess air will try to get out through any spaces/holes in your case. More air in than air out=less dust. I have an H440 so can't be a huge help with the S340, but I do have an X61. If it doesn't seem to fit, try twisting it around and trying it in different positions that you can, should be able to get it to fit easy enough with a bit of maneuvering.