If you are using the
SM plastic box set captain that you are in good shape. You should be able to find the
=I= shoulder pad bit around for him as well that comes with the terminator boxset. Remove the winged jewel, skull, eagle thingy from his chest... that is very Adeptus Astartes. After that you should be in good shape. Really all that is left is to make him unique in stature, and or decoration to the rest of your army. I dig the idea of using a Arcoflaggellant head. I have never seen that done before, and will add a creepy, mysterious tone to the model.