Either way...now thinking about it..swapping svt motor for a ported 3l i would stay with 19's. But if he's getting a tune done anyways i would go with 24lbs.
I just know people with 24lbs who ordered a tune..had problems getting it running right. So i didn't want to see it happening to him. To play it on the safe side i'd rather him get a tune for the 19's which have been done tons of times. And leave the 24's when he can get a in house tune done.