You are going to remove that heatsink. Pretty much because of it's location, it's almost flush with the board. Getting it down half an inch would keep it from making any contact, but if possible try to remove the whole metal block and put a new block where the new processor is. There is really no way around due to it's location. Also the design was made to use the chasis for heat dissipation. You maybe able to slip a small heatsink in there, but it's not going to work very well.
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