I was a bit worried that we would have to do some modding and drilling of the clips due to the VF1 Plus not being compatible with the X1800 series. To our surprise and delight, the medium-sized clips fit perfectly. After applying a thin, uniform layer of Arctic Silver 3 on the graphics processor, and wiping a bit on the sink to fill in any microscopic pits, we thought we were out of the woods as far as compatibility was concerned.
Unfortunately, modding uncertified hardware is rarely that easy. Although the bolt pattern matched the card perfectly, the heat sink refused to seat properly. Upon close inspection, the reason became apparent; the two tiny screws holding the mounting clips to the heat sink were interfering with the graphics processor's spacer.
The spacer is a square, metal rectangle surrounding the processor, used to ensure that a graphics cooler won't put too much force on the edges of the processor and damage it. The tiny screws holding the clips to the VF1 have a convex head and would contact the spacer before the sink could properly seat. The screws were only stopping the heat sink about half of a millimeter from the processor, but in cooling terms, that might as well be a half of a mile. Something had to be done.
The first strategy I tried was to remove the spacer (don't try this at home, please). I can remember doing something similar with a Radeon 9700 Pro a long time ago, when I removed its spacer so the heat sink would make better contact. On the 9700 it was not a walk in the park - it is always a bit unsettling to physically alter a video card with tools and force - but it was doable. Unfortunately, the glue used on the X1800's spacer was, by my guesstimation, 10 times stronger than that on the 9700 Pro. I tried to pry it using a knife, with as much force as I dared, and had absolutely no success.
Short of milling the edges of the spacer I wasn't sure how I could get the VF1 Plus to fit. Then it occurred to me: the screws that were causing me a problem were convex... I wondered if I had any flat, countersink style screws to mount the heatsink with. After a few minutes of searching through the 15 years' worth of spare screws in my computer junk stash, I found them. They worked! Success!
The hard part over, I smugly installed the card and attached its power cable to the test bed.
Spacer and screws interference diagram