Wow. Lol I always assumed you couldn't get grabbed during the cargo. That's pretty dumb.
Anyways I got some results on the side b. The formula so far looks like its 96+D-5N= frames of pitfall stun for grounded headbutts. For aerial headbutts the formula is 114+D-5N= frames of pitfall stun. D is damage after the headbutt and N is the number of button inputs. Grounded headbutts have 8 frames of hitlag and aerial headbutts have 10 frames of hitlag so overall the aerial headbutt gives 20 more frames of hitstun after factoring in the extra damage and hitlag.
Anyways I got some results on the side b. The formula so far looks like its 96+D-5N= frames of pitfall stun for grounded headbutts. For aerial headbutts the formula is 114+D-5N= frames of pitfall stun. D is damage after the headbutt and N is the number of button inputs. Grounded headbutts have 8 frames of hitlag and aerial headbutts have 10 frames of hitlag so overall the aerial headbutt gives 20 more frames of hitstun after factoring in the extra damage and hitlag.