Hot air is going to rise up through the top of the case, pushing air back in from top down is going to create a double strain on the blades plus is going to keep the case full of hot air, bad idea.
Putting the rad on the top is going to make all the hot air pass thru the fins of the already hot rad thereby reducing it's efficiency, again not a good idea.
Mounting the Rad on the back and pulling air into the case is the best option.
Since you already have 2 intake fans and 2 exhaust fans, a set of fans pulling and pushing air into the rig is going to create a positive pressure in the case but since it's hot/warm air that is being pulled in, it'll immediately exit through the top, creating a negative pressure, which is good for the ambient temps within the case.
Mounting the rad might be a little difficult since it twice the length but it can be mounted on that case.