I'm pretty sure that if you use LBSTEP to provide neck protection to critters wearing it, it will still protect the actual head, which is a little odd for a gorget, however, I think this can be counteracted by setting neck bodypart to have the [HEAD] attribute and adjusting the other head armors to have an appropriate UPSTEP value so that the head will still be covered. since the head contains the brain, critters will be die upon decapitation, but removing the neck will also work to this goal, since if the lowerbody, upperbody, or head parts take critical damage, the creature will automatically die. Another thing to keep in mind is that a creature can wear one armor from each armor level in DF mode, so if you have a -cat leather coif- (armor level 1), a +copper gorget+ (armor level 2), and a -steel greathelm- (armor level 3), you can have a dwarf wear all three at once (this goes for all body parts). The prerequisites for this to work are that you adjust [LAYER_SIZE] and [LAYER_PERMIT] to make sure there is enough space on a given body part for all three to be equiped at once. Also, keep in mind that only one item with the [SHAPED] token can be worn per item type. hope that hopes, my memory might not be perfect, it's been a while since I have been modding DF.
A sample:
[ITEM_HELM:ITEM_HELM_SCALECOIF]
[NAME:scalemail coif:scalemail coifs]
[WEIGHT:10]
[VALUE:14]
[ARMORLEVEL:2]
[BLOCKPOWER:40]
[LAYER:ARMOR]
[COVERAGE:80]
[LAYER_SIZE:10]
[LAYER_PERMIT:35]
[MATERIAL_SIZE:1]
[METAL]
[HARD]
[ITEM_HELM:ITEM_HELM_BURGONET]
[NAME:burgonet:burgonets]
[WEIGHT:22]
[VALUE:16]
[ARMORLEVEL:3]
[BLOCKPOWER:60]
[LAYER:ARMOR]
[COVERAGE:80]
[LAYER_SIZE:15]
[LAYER_PERMIT:35]
[MATERIAL_SIZE:3]
[HARD]
[METAL]
of course, if you want these to cover the neck, I'd think you'd have to add LBSTEP 1 ore something.