I would personally go, as suggested above, for the Varangii-style helmet, great big aquila on the chest, togas and capes. I don't see any reason why you couldn't include bolters, though there are absolutely no descriptions of them firing a shot, that I can remember anyway (just finished Fulgrim again).
If you don't give them bolters, then just count them as twin lightning claws, owing to their perfection in battle (or somesuch...).
I believe their halberds have golden blades, and that's just about all the details you get out of the book (no doubt vespasian will soon correct me though...
Oh, and I'd stick a sweeping wing on their left shoulderpads, like their primarch (instead of just painted on).