I encountered same troubles with RAM sink, just cut it with dremel. AC S1 is a... cheap heatsink, you'll have to adjust things so that they fit well. I did the same for PWM heatsink but I couldn't use the standart thermal tape and use arctic cermic but it doesn't touch the PWM chip well... I need to find where to buy this kind of thermal pad such as those you get with the stock heatsink...