I find Hornet's bare heads ( in this case the type without hairstyles ) to be very useful especially with helmets. If you're on a budget one set goes a long way. Here's one I used on Dragon's Marine. Attaching it on an opened collar or bare chest requires more work than a buttoned or closed collar. Putty was used to patch up the joint.
Here's the figure posed with the others also upgraded with bare heads.