Decided to thin the IHS on my 13900ks. Used a belt sander and then cleaned it up by hand using sandpaper. I went 120>220>320>500>1000
I also had to thin the contact frame otherwise the cpu would no longer stick out above the frame.
The results speak for themself. I can now easily cool the 13900ks. Using a TR Phantom Spirit Evo 120 and Duronaut paste, I can cool a package power of about 350w on air with an ambient of ~72F. I unfortunately don't have a waterblock or even an aio to test further.
I did not modify the cpu cooler mounting bracket for more pressure though. I suspect once I do that to add more pressure, I should get a few more watts of cooling.