In this post, I have glued the heads and arms to the resin bodies. I used superglue and some modelling filler to fill any gaps, particularly around the scarf/neck area.
I found that the heads needed some careful trimming from the resin casting block. I cut the blocks to the shape of the neck (a tube shape running from the head) and then trimming them to length was the best way forward. The metal arms and guns needed some cleaning up, but nothing too difficult.