you can still use mitsu s90 tb but u need to mod the vtec intake. i think it will be much better to use mitsu s90 tb because you can use back your stepper motor and tps sensor. much easier.
one more thing, if u use s90 tb, u will experiencing some idling problem, because the s90 tb dun have sensor like what mivec tb. but dun worry, u can use 4g93 tps sensor. if u r lucky, then u wont experiencing that problem.