As I've been making various remixes and costumes for the wonderful Dummy13 by soozafone (/model/593185) I've created some stls that might be useful to other people. This model serves as my repository of these files and may be of some use.
Solid Neck - This combines the neck-armor and neck-frame into a single piece. Note, this also removes the slight point on the back side of the armor piece.
Shin-Amor - This is a slightly beefed up version of the shin-armor to make it easier to print and less likely to break, by just making the shin wider at the ankle connection side.
Forearm-Armor - This is the same mod, just for the forearm.
Broad-Chest - A much broader chest for superhero-esque physique