I have done Frenchies in the past but have opted for 1 arm pullups from fully extended (hanging) to 90° (120-90° is the usual elbow angle for these sit starts),
with a weight/pulley to help, also because with these, like the sit starts, your palms are facing inwards.
Now I just have to reduce the weight from the 20kg with which I can do 6 (meaning -10kg of bodyweight) to zero
. Though my book says if you can do 6 with a 53 (63-10) weight, you should be abe to do 1 rep with 63kg weight i.e. no assistance...we'll see...
Peter