Yeah, none of the Manifold upgrades will let you stay in ST Class.
I like to add a good suspension set as well. Stiffer suspension or something adjustable.
I am currently looking for better suspension.
As for tires, make sure you are ready to REALLY test them. I thought my Yokohoma S.Drives were great and grippy ... but once you put it to the AutoX test ... they didn't do as well.
Will this be the first time AutoX-ing?