my guess is they just werent a cost effective mod. for NA its easier to go boost for extra power. and when SC you can go turbo and make more power. also there are stories that when you try to build the bottom end on these engines that they dont last long. i have read a bunch of threads where people have spent big money on a shop and parts to build the bottom and still have the engine last less then 1000 miles. that being said... messing with the bottom end to put a stroker kit in sounds like a risk. also the other options for power are easier to install as the engine doesnt have to come out.