For the instrument I choose a horn with the icon of Khorne on it form the Bloodletter sprue. I cut the hand off of the model and filed it down. I then glued it to the back of the Bloodletter. To make it look a bit more like I didn't just glue a horn to the guy I rolled out a thin rope of green stuff and fashioned strap for the horn. I originally tried a piece of guitar string but it was to firm and kept popping out. The green stuff proved to be much easier to work with.
I already had one Crusher done and as I started putting the other three together I realized that they were all going to look very similar. Aside from giving this one a horn I wanted his head to be different.
I had this face leftover from a box of Bloodletters. Since I didn't have a spare upper head piece I used the one that came with the Bloodcrusher. It was a bit tricky to get these two to stick together since I was gluing a very thin area of pewter to plastic, but when I added in the green stuff it became solid.
All in all this was a pretty easy conversion that added some flair to my unit and helped them stand out from each other.