The choppers need no crediting.
Essentially:
Guns/turrets(any weapons really), FC, choppers, planes, boats, small detail parts(life rings, lockers, fire fighting equipment), and so on does not need crediting.
If you use the hull, superstructure, or otherwise large "bits" of someone's drawings, then you're expected to credit.
It's a really confusing gray-zone, but you'll get it soon.
On a small side note on the use of other peoples' drawings: You are allowed to use any drawing on SB as a basis, or take parts from any drawing for use, as long as you credit correctly. If it's a Real Life of Never Were drawing nobody can really protest, but if you're using parts from someone's Personal Designs or Alternate Universe, it's usually prefered that/expected of you to ask the artist first. Most people will probably say yes anyways, but not all, so it's best to ask in case of a PD or AU drawing.
And again, for a beginner, you've displayed exellent talent for adding details. Best of wishes for you!