The Axial Twist:
Kick propulsively while rotated at about 45 to 60⁰, keep both hands at thighs while breathing. The goal of excellence is to keep both the kicking feet and upper butt cheek at the surface, and breathe continuously with one goggle lens UW. Fins work great.
Head-up freestyle with fly kick:
I use a snorkel and fins, the aft end does its action naturally, but for the upper body it's a vigorous game of catch - pull - catch - pull. Of course fins and snorkel work good doing these.
Wear snorkel and use fins to get you moving at a sufficient speed with arms back (hands at thighs). Do a full stroke: Rotate and recover up arm, counter rotate and catch, following through with a pull but keep hands at thighs kicking several times, still rotated, ready for next arm. This drill helps me connect the energy transfer from rotation to shoulder to catch, as well as pulling the hand in a proper path.