The original Choc Anon graft was done by the nurseryman where I got them from, I did not graft them myself. I only grafted the Lemon Zest so I don't have actual experience to give you pointers... but it really doesn't look that difficult if you're familiar with veneer method.
I thought it's interesting grafting onto a variety that produce multiple crops. I've never tasted Choc Anon but going against Xoài Cát Hòa Lộc and the likes, I don't understand the fascination since most farms induce their trees for out of season fruits anyway?
Good luck with your graft Max, keep us posted.