It's very easy. Both arms are separate bits. The joint is a flat surface, exactly like in the plastic warriors, so any plastic arm might fit without much effort. I took this pic for another thread for a scale question, but seeing the bits might be useful for you. Sadly, the pic is so crappy that you might not see a anything
The 3 bit sprues above the minis belong to the Archon blister. They are: backpole thingy and right arm, both models of heads and left arm with sword. And the minis are the Twilight Knight Pinup by Kingdom Death, the Archon's body and Laelith Hesperax.
Cheers!