I've only done 2 onto mamey, but what I was told (an seemed to work) was to use scion wood that was still pliable or a bit "cheesy" with a swelling terminal bud. Use a vigorous rootstock that again hasn't really hardened off. If the bark is still grey/green and smooth/shiny that was supposed to be better than if it had become woody/fissured already. That said only 2 of 4 took.