Planning to start a 40k CSM army with the 30k Saturnine box. Supposedly I can use the 40x Mk2 marines as some combination of Legionaries and Havocs based on weapon loadouts? The Centurion can be used as Abaddon, the Saturnine terminators as Obliterators, and the turret as a Defiler with some kitbashing.
What should I do with the Saturnine Dreadnaught and the Saturnine Praetor?

Building a The Scouring themed Ultramarines army using the new heresy models.

Would the Saturnine Praetor be a good counts as for a gravis captain/marneus calgar?