After careful examination of the allignment, i have come to the conclusion that the AM4 holes are offset on the ASUS Motherboard. EK stuff looks straight enough. But even the back plate is slightly tilted. And yes, these are the only AM4 holes. AM3 is too far away.
I finally managed to get the bottom radiator mounted. What a hassle that was. I used velcron underneath and bolted the top sides at the rear. It feels very solid. And thanks to the velcron it will also dampen any excessive fan noise. I'm quite happy with this solution, as it is both very sturdy and secure. It will withstand any force applied by waterpumps or movements of the case.
I also found the original bag with all the Cosmos II parts. Keeping it together in one place paid off.
Now i can focus on getting the reservoir into place. I might have to connect all the HDD cables first. i'm thinking about replacing all of them. But that can also be done at a later stage. I still have my 20% discount voucher from Cable Mod. I can use that for a full replacement cable mod kit for the AX1200 and some SATA Cables. Plain Green might be the best.
But right now i will stick to the extender kit for improved visuals, while i try to finish this project. After the waterloop build i still have to do a lot of hard and sofware upgrades, BIOS flashes and not to mention all the games and gear.
But that is a piece of cake compared to the raw building and test fitting.