And we're up and running (despite encountering my first leak ever... from the fill port on the cpu block of all places).
Part A: rotated CPU block w/ ultra short tubes; note that if ASRock had a temperature header on the motherboard, then I'd be using a temp probe stop fitting on the fill port instead-
Part B: 120mm fan cooling motherboard while in 3-slot GPU config-
and then I failed Part C, which was trying to push the radiator close enough to the back so that I could use a 90-degree fitting on the Coolworld fill port (placing a fill port at the top/front of the case). I can make this work if I opt to remove the wifi/bluetooth card (which would also make the tubing easier to fit), but not sure if having access to that port matters that much to me since the one on the cpu block works well enough.
My biggest issue at the moment is that my pump has been dying for a while now (or I think it's dying), to where I have to tap on it to get it up and running sometimes, so I can't really firm-up the fan mount until the Aurora LT Solo becomes available. Beyond that- just need to firm-up the PSU mount and possibly get some shorter cables/do cable management, and I should have a pretty clean build.
edit- played new world (uncapped) for 45 mins before making the change/after: fan at 1250rpm results in 12c drop on motherboard, 18c drop on PCH, and 20c drop on ssd.