Due to the screws not wanting to reseat on my old heatsink, I just got a new heatsink and shroud kit to try again.
My Noctua fan did not fit onto the new heatsink either. So, I took some calipers to the various mounting posts and the fan holes. It looks like the inner distance between the mounting holes on the fans are just a fraction of a mm too far apart to fit on the mounting posts without some force. The typical inside post-to-post measurement was just around 101mm with a couple just under by a 10th or so and some over that by a 10th or 2. The inner fan hole-to–hole distances on my Noctua measured around 101.3 or .4 meaning they did not have clearance to slide over the mounting posts.
More time with the dremel and a new cylindrical bit and I was able to shave the inner sides of the holes on the fan so that they were less than 101mm apart and the fan now fits with no force onto the mounting holes.
One thing I noticed when screwing in the new fans and shroud, I never got much resistance on the screws. They just kept screwing in and in but the fan was tight against the heatsink. I decided not to keep turning them as it was already tight enough, but shouldn’t they have seated and provided some resistance? I seem to recall this happening with the original screws and heatsink and now I’m wondering if I may have stripped the original screws and that’s why they wouldn’t re-seat after I removed the fan for the M.2 swap. Anybody else notice that the screws never seemed to fully seat?