rear diff carrier and some allowed suspension (brake?) component swaps between years with same body but different engine is a big SM allowance difference from IT. SM has to maintain more stock components and only recently was allowed over-bores and the like and then only with added weight.

you see a fair amount of double dipper SM guys in IT who are in breach of IT rules. I'm sure you see the same in ST. ST requires one hell of a scrutineer.