I concur with the six people above me to reject the idea of using a single 120 rad for both the CPU and the graphics card.Here is my analysis:
2500K @ stock 3.3GHz has TDP of 95W.
HD7970 @ stock clock consumes about 195W.
Total combined wattage to be dissipated ~= 95 + 195 = 290W
Using Skinnee's chart for RX120 and assuming the watercooling system is an average performance system (ie having 10C Delta), the fan will need to spin at around 2700rpm.
(chart source: http://skinneelabs.com/xspc-rx120-v1/4/
This will be quite noisy, IMHO. If you add another fan to do push-pull, it will probably bring about 20% more performance. But I think the noise level will remain at a relatively high level. Also note that neither the CPU nor the graphics card is overclocked. But, of course, both are unlikely to be fully stressed simultaneously in a real world situation unless you purposefully put both under a loading test.
So, as the general rule of thumb says, better allow a 120 rad cooling capacity (at the minimum) for each component.
Stacking/sandwiching two rads usually is not very effective. See the reference below for some numbers.
I would much prefer using a 240 rad or putting two 120 rads at different locations of your case. For your TJ08E, it is going to need some creativity and/or modding.
Reference for stacking/sandwiching rads: