all s series are non interference motors. there is still a chance of whacking the head and or valves but it is very slim.
when i bought my gts it had a shreaded Belt. that had slipped. i believe it had like a tottal of 5 teeth left. I slapped a new water pump and all new belts and gaskets on it. and that motor has been running fine ever since. to bad its in my brothers GTS now but hey. my work has proven to be worthy lol