I don't think that's such a big deal, the word "conversion" is quite wide.
SH3 and SH4 are different but the Atlantic was is still the same, when people talk about conversion it's (IMO) about porting the truly great and torough work of a few people on the SH3 campaign into the SH4 layers, with as much additions as the new engine permits.
It's not really about "porting SH3" but really about porting as much as the atlantic as possible for those (like me a bit) addicted to that theatre.
Peace
