Trying to Mod a VGA Heatsink Cooler.

I have a geforce6800 agp, the cooler is 99% the same model as the 9800gt model (this model is way better because it has copper think metal)

Because the 6800 is AGP, it has the (HSI chipset ) https://www.quietpc.com/zm-vhs1
On the 6800 heatsink, the big heatsink also covers the HSI chipset.

i wanto to transplant the 9800gt cooler and heatsink into my card, i just need to sand a little bit with a lime a little bit where the HSI goes. I noticed that the original cooler heatsink also had like a "cloth" that touches the HSI with the heatsink.

what material is that? i never saw something like that. only saw memory heat transfer pads that were flat and soft. but this material is like a cloth and more solid.

Can i replace the HSI cloth with a regular Heat Transfer Silicone Pads used in ram chips?
is HSI something that produces a lot of heat? I dont want to burn it.