Max,
Impressive so far. That part you pointed out is actually supposed to tuck in on the chest. The nose section's attachment level was different in Battroid mode from the Fighter mode. You could tuck that in and then trim down the rear part of the spine to match it. That would give you a better look IMO.
The head block's mechanisim looks more complicated than it has to be. I think there's an easier way from the look of things in your pics.
PM me if you're intrested in my thought on the head block. I can send you a sketch.
The upper torso hinges look like they need a re-design for function as well as a re-texture to match the functioning feature.
Also keep in mind the posable arms are bigger than the Fighter mode ones as well as the Battroid ver. B.Pak so those may pose a problem for you. The smaller B.Pak may be needed and the arms should work as is but they will limit the clearance for the GU-11 (much like the old 1/72 plastic transforming kits).
I take it you will use the extention bar method for the legs? That's probably your best bet there
You still have a very long way to go still but things are looking promising
Keep up the good work.
G1