Will this work?

Ok so im gonna be running 2 xfx 390s in xfire I want to water cool but it has the new inductors (the z not the c) soni cant find a full block that can fit. So my question is this, do I have to have a full block or would something like a EK-VGA Supremacy gpu block work and just use the passive heat sink that came on the vram? I dont plan on oc I just want temps down a little 75c (170f) is to much heat. I havent bought the case yet and also considering a Thermaltake Core P5 ATX Open Frame (are they any good?)
Specs
Cpu: I5 6500 WC CORSAIR Hydro h75
Psu: XFX ProSeries 1000 watts
Case: Cooler Master HAF 932 Advanced
Mobo: ASRock Z170 Extreme6
Gpu's: http://m.newegg.com/Product/index?itemnumber=14-150-729

This was just posted today, good to read a bit first:

He ended up getting another card anyways.

http://www.overclockers.com/forums/...lock-for-GPU?p=7902826&viewfull=1#post7902826

Ok but thats a completely different card from a completely different company, and it doesnt say if its dangerous or how the temps would be and I don't have the option to go out and purchase different cards. I have to work with what I got

Cards are cards, GPU is GPU. You need to cool the VRMs as well as possible and some cooling on the memory. It's always possible stuff can happen.

You might find more info in the GPU subforum too.