You could just remove the RAM heatsinks, which rarely have much benefit, just do it carefully. Then you can choose whatever HS you like. Improved airflow from a bigger/better HSF will more than offset any potential loss of cooling with RAM-sinks removed. But as I said, there's little evidence to show those things really do anything anyway. It's mostly marketing.
Or look for something that fits -- maybe one of the Zalman radial towers like CNPS9900. http://www.silentpcreview.com/zalman-9900max-cnps5x
At 1000rpm or lower, the fan on the 9900 is decently quiet (under 20 dBA). The CNPS5X also reviewed in the linked article, will fit as well, though it does not cool as well.
You could try the stock Intel cooler. Maybe with the fan dialed down, you can achieve a reasonable balance of quiet and cooling.