To the best of my knowledge, that humpback handle is only available on the new #4-6-"F". The tang is forged and shaped differently on this model. That's why there are no other handle shapings available on the new #4 fighter.
Best, Capt. Chris
PS: I'm glad ya'll liked the pictorial...CCS
PPS: Another Model #4: This time with a #22 / crow's beak combination...