I don't recommend reapplying the x-clamps, as they are most likely a contributing factor to the RROD in the first place.
One bolt through the backside of mobo (no washers, washers raise the center of the mobo up more in relation to the standoff's that encompass the inside edge of the metal cage = instant flex)...on the topside of the mobo, one nylon washer, then one metal washer, then the heat sinks.
Speaking from experience, over 200 reflows performed, have never reapplied the x-clamps.