1. bulkheads should be a direct fit to the g4 chassis.
2. FLM have redesigned their shock towers to use the newer square style body posts- probably just an old picture various websites selling them.
3. FLM 3905 motor mount will fit the 3905 tranny perfectly, but it may limit the size (height) of the battery you use on one side. Should be fine for anything upto a 3s lipo, but a fatter 4s or larger item may be a little too tall. Maybe...
4. Aluminium skids are fine up until the point you bump into a tree or curb, then they bend very easily:
I would look around for Ti skids- ebay or forsale sections of forums (NewEraRacing sell a Ti rear, but no fronts).
Emaxx parts are very universal, at most things just need a little filing or dremeling for clearance, but its rare.