I have not installed any rads in the ProM tho had no issue withe the Primo, Luxe, Evolv and Pro. You have two choices with regard to fit:
a) Contact Phanteks techsupport for dimensions
b) Buy the case and measure yourself ... I don't have one here or Id measure it for you.
I did note that the A40 has the fans installed contrary to the 1st rule of water cooling .... they are installed as exhausts.
1. Do you really wanna cool your CPU with preheated case air or cool outside air ?
2. Are you planning additional case fans ? As delivered you have (1) 140 in and (1) 140 out ... because if the air inlet filter restriction reducing the air flow, you will have negative case pressure. That means 2 things will happen:
a) The negative case pressure will suck in outside air thru the rear case grilles. That air will consist mostly from hot air exhausted from your PSU and GFX card.
b) Carried in with that hot exhaust will be dust.
3. Solution is to move the rear case fan to the front or add an additional front fan.... Problem is now you are adding two more exhaust fans and much faster noisier fans that move more air with the A40 which will triple (or more) the negative pressure situation ... Solution, flip them over and use them as intakes and use cooler outside air into the case.
4. Other issues ... what's happening with that 3rd top fan location ? Won't hot air exhaust just get sucked right back in ?
5. I would consider, an alternative:
Swiftech H320 X2 top radiator ... this AIO, unlike the CLC Cryorig, is expandable, has copper radiator, no mixed metals, pump is 10 times more powerful, and
is expandable.... and eliminates the issue with the rrd fan location.
http://www.swiftech.com/h320x2.aspx#tab5
This allows you to water cool your GFX card with a full copper water block from EK such as available pre-installed on 1070 and up...
https://www.newegg.com/Product/Product.aspx?Item=N82E16814127956
This gives ya the same radiator area as the the A40 + Hybrid GFX card would... but with the Swiftech, copper instead of aluminum, no mixed metals, less than half as loud, better temps, and one single system that moves 5 times as much coolant as two separate ones.
If you chose to, you could add a 2nd rad in the front.
To get the dimensions, the Phanteks site says it fits 120 x 360mm rads and 140 mm x 280mm rads so it should fit
The unit's dimensions are
127mm wide (case fits 140+) x 375 x 28 mm
If still concerned, I'd suggest asking in this thread here... I posted all dimensions of interest in this thread for other Phanteks cases. I am sure one of the users with the Pro M would be willing to supply the necessary dimensions.
http://www.overclock.net/t/1418637/official-case-phanteks-case-club-for-lovers-owners
You also might consider the Enthoo Luxe... especially the new Tempered glass model.... it has an "attic" into which you can install the fans which gives you an extra 25mm. Here's a pic of a custom Enthoo Luxe Build we did with the H240
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