I say do it! It would be awesome if you can get RADs on the cheap.

You could bend your own brackets if the rads were together and the fans on outsides (front and back in the case. Make 4 out of flat thin 3/4" to 1" wide steal or aluminum bent into a [ shape with mark the holes and drill them slightly over size to allow for a small margin for error run the bolts through fans then bracket into rad holes. Same on the front except through case holes then fan then bracket into rad holes.  Fans/rad/rad/fans/case front. You might have to stagger them slightly to attach you water tubing or flip them, water ports up on one and down on the other. A cool idea!!
Edit: After a closer look at that those rads your port position is optional that should work nicely.
Go for it!
I was considering that on my 140mm rad in the back of mine.

The manufacturer say's slow to medium speed fans perform extremely well. I would think a push/pull setup would work great.

lehpron

Thermodynamically speaking, a radiator is just another type of heat exchanger where heat from one medium and transfer it to another.  Best case scenario is when the input air is coldest, then the exit liquid is at its lowest.  But stacking up the radiators forces each additional radiator to receive the heated exhaust from the one before it.  So the liquid won't cool as much, but you'll have to do your own experiments to be sure if the difference is worth the space savings of stacking them.

If you stack too many radiators, the last set of radiators isn't radiating any heat from the liquid since the heated air coming in to probably too close to the liquid temperature in.  Once the temperature of both air and liquid inputs are the same, they exist at the same temps, there is no heat transfer except for whatever the radiator absorbs such that it feels hot.

I agree they would work better separated but I would still think it will perform better with proper air flow than just one rad.

How are the fittings going to look on that thing?

OK, I have built a few stacked water setups over the years, including the Swiftech stackables. 
What Lehpron said is 100% right, however, it really doesn't effect things much in a 2 rad config, maybe 3-4.
Now,, what afterburner said about the Swiftech running fine is true, however, it doesn't take much to go from fine to really good. 
First step you either need multiple fans or a STRONG center, even on something like the swiftechs, as you have resistance on both ends. 
Next, and I CANNOT STRESS THIS ENOUGH, run the radiators in series NOT parallel.  Yes, I know that the instructions say to run them in parallel, but don't.  One of my loops is with the Swiftech stackable 360's, their instructions didn't seem right but I assembled it on a work bench, and it worked OK.  The rads were warm to the touch (not hot, just warm) and the parts were the temp of a stock air cooler.  I changed the config to enters on one rad, junctions to the other rad and exits the second one.  My CPU temps dropped SUBSTANTIALLY.  I ran a setup like that on a OCd X58, mobo full cover block and SLI and it did really well.  Was it the best loop I had seen, nope, but it did better than many.
When it was on a test bench I swapped it from serial to parallel about 4 times to make sure and the testing was the same every time, obviously there is always 1-2c degrees variance, but nothing substantial, but there was always a definite gap between serial and parallel.
 
The rads you linked are pretty thick, but I did not see a rated FPI, if I missed it, please someone let me know, but in general, look at something like AP15's, good balance of pressure/noise.  However if these are high FPIs like GTX Extremes you might want to use like AP29's or AP30's and a fan controller. 
Wait, these are 140' rads not 120, you can use the 120 adapters, or look over Boredgunner's fan thread for some good 140 options.  Unfortunately, 140 never  REALLY took off, so the selection of good fans is not nearly as good as 120mm fans.

Here's a horrible paint/sketchup drawing of my plan.

 
It will be some kind of version of that. with the front of the case to the right.

Thought about a controller like this http://www.frozencpu.com/products/12481/bus-247/Sunbeam_30W_Rheosmart_6_Channel_Smart_Fan_Controller_-_Black_PL-RS-6.html?tl=g47c17s240

Thanks for the input everybody. Now I just need to get the cash for the rads, and to find some short M3 screws to to put everything together. I will post pics of everything when I get it done in my Mods Rigs thread.

That would be a solid way to do it Nate.  Keep in mind, that i have seen this specific rad brick in action, and while you are correct about hot air, its basically like the old PA 120.3 as it is a dual pass internally, this is done with 2 physical boxes, and I can vouch for this specific setup like this, that it cooled well.
Would it be better to run the separately, sure, BUT, in many cases without severe modding its almost impossible to get 2 rads this size, internal.

zophar

This is the inside of my case as it sits now,


There will be a 420mm rad in the top, and the 280mm on the front. I was just thinking about running the double stacked 280's in the front for a bit more rad surface without doing much cutting. If I need to I could place one 280 on the front and another 280 on the bottom with a little bit of cutting to fit it. But like I said the idea was more rad surface area with minimal modding.

for SHAME?!?  who wants to do the MIN??

My machine isn't too far off in the horizon.  I think I have all but one component left, then to put it all together and pour 800 lbs of concrete.

Well got my 280mm rads a couple days ago and got everything bolted in. It'll still be a while before I can test evverything since I'm still lacking my top rad, PSU, and a handful of fittings. But here it is as it sits now.
 

 

 

 
Now I need some black stop fittings and to figure out how I want to connect them together. I was thinking about one of these (http://www.performance-pcs.com/catalog/index.php?main_page=product_info&cPath=59_346_393_621&products_id=35192)  to put it connect the rads, but can't fing the length or anything.

+1, I gotta say I'm curious about this one too. I'm going to assume that since he never posted back it must have worked out pretty well.

Have no fear I am here lol. Wow this thread is old. It worked out fine. I did recently un stack them and put the second radiator off the back of the case. The main though behind stacking them was to keep everything in the case. It does hinder thermal efficiency slightly, but the Alphacool radiators do have a fairly low FPI count which helps. Surprisingly I didn't have too much of a problem with dust getting trapped in the middle of the radiators. I will say that when I separated the setup I did see about 2 or 3 degrees drop in temps. Now 2 or 3 degrees on most systems isn't a big deal unless your going for a max 24/7 OC. But on my system it didn't affect anything.