teg_fan is right. you can use stock valve train but skunk2 recommends you upgrade it even for the stage 1's. but if you don't you can still run the stage 1's.

i'm not too familiar with the crower stuff.

as for the itr or ctr. you don't need to replace your stock cams cause those aren't as aggresive as the skunk2 units or some other aftermarket cams. but the itr does have stiffer valve springs. just depends on how in depth you are tryin' to go with this install.