The conversion process involved cutting the weapon haft away from the hands and then cutting off and rotating the left hand. The weapon haft that was between the hands was added below the hand to form the base of the weapon haft. The other bits included a green stuff blob on the models back with 6 cut off exhaust outlets from some leftover SM backpacks.
The extra bits on the Manreaper came from a Bloodthirster kit, the blade chopped off the BT Axe and part of a whip handle to form the rest of the weapon haft. I also found some extra skulls from an old CSM Rhino which I applied in various places. The skulls on the end of the shoulder pad spikes were from a Bloodthirster Khorne Banner.
Deathwatch models definitely coming in handy for converting my Deathguard - haven't used them for anything else. Next DW to get the Nurgle treatment will be a Dreadnought.