I tweaked the back 3/4 frame again. What I did before just looked wonky to me, so I captured the model rotated slightly more towards the side to match. It's not exactly how Uekawa drew him from that angle, but it just looks better. I also brought the shortened the middle quill on both that frame and the back frame.
Here's a preliminary running animation:
It's still mostly traced from the model, but I adjusted the position of his arms and feet in a few frames to more closely resemble the Advance 2 and 3 running animation. The head position was traced and modified from a single frame of the SA2 model running animation, but instead of having the head rotate and bob, I just animated the quills and the ears like in the Advance games. The head and body are separated in my GIMP layers so that I can adjust them all when I'm done shading the body.
Getting the adjustments consistent in the rotations will probably be annoying, but since I have the model as a base, I assume it will be less so than doing it all freehand.
Don't expect it for quite a while. The art is taking a long time, and I haven't even fully animated the standard running rotation yet.