Need help with making a proper DG army based in my Warbands Lore

So basically the custom warband I created called the Cancerous Sons(check out my other posts to see them) who mainly use Terminators, Dreadnoughts/Helbrutes, Vehicles, with some support from normal plague marines. I was wondering, what dreadnoughts I should use for the ranged and melee units. Idk how the rules would apply to these dreadnoughts, would they have a helbrutes stats or would they have the stats of their loyalist counterparts? For example if I used a leviathan dreadnought for my melee DG dreadnought would I use the rules/stats of a helbrute for that dreadnought or just the normal rules/stats for a leviathan dreadnought?