Well that was fast!
After playing around with some Green Stuff, I have completed the first arm!
This took a lot longer as I am still very much a novice when it comes to sculpting. However, all things considered, I am happy with the result.
As for the second arm, I decided to re-pose the claw as it was drooping down quite significantly. I clipped the claw as best as I could to avoid collateral tissue/chitin damage, then after a bit of clean-up with the hobby knife I drilled and pinned the claw back on at better angle. This was followed by a fairly successful Green Stuff fill-in.
I still have a bit of cleanup (mold lines, etc.) to do on both arms, but will wait until the Green Stuff has dried.
Pictures below. Hope this tutorial was actually useful!
(As a side-note, since I had to do sculpting anyway, I managed to finish magnetizing my Tervigon arm sockets, as well as all 3 sets of Trygon/Mawloc talon sockets, as well as the Trygon/Mawloc head carapace, jaw area and pincer sockets! I still need to drill and magnetize the talons, pincers, and remaining head carapace, but all-in-all a productive day!)
Finally, a pic of the Devourer on my Carnifex... and yes, I do realize that the radical angle I decided to place the arm magnet is a bit odd. Live and learn.