I bought a squad of snap fit Reivers to convert. Ran out of steam before I got far:
I cut down the small shoulder pad to fit a Deathwatch one on (since I have no better place to put Primaris than my Deathwatch).
As you can see I'm not thrilled by the power shorts so I gave hydraulics a try to account for their deep strike option. More for fun and seeing how it would look than anything else, really.
And at that point I put so much armor on that I thought rounding it off with the little heraldic shield couldn't hurt. Not that armor overload matters since they still wear fully enclosed power armor with a 3+ save just like everyone else.