
The lower arm is cramped with polycaps, some planning with drawings is needed to make sure there is enough space. With some luck, pretty good mobility can be achieved without too many trial and error. A final thin styrene sheet is used to add the surface detail (notches) on the side of the lower arm.

You may notice the bolt of the elbow is attached to the upper arm, instead of the lower arm as in the stock kit. You can saw off the bolt carefully using a saw scriber and glued onto the upper arm with the elbow joints locked in the upper arm. This is not the best arrangement since the entire arm are now in one piece and need extensive masking for painting.
One advise I have is not to go crazy when beveling with the sand stick. Care must be taken to check the surface after several sanding strokes. Or else you may have to putty and resand like I did here.