How do I train a seedling Lemon Zest mango?

My Lemon Zest seedling has about 4 shoots all with tight crotch angles and is growing rapidly at about 4feet tall. I know LZ is vigorous so this seedling will be also. How do I train or prune it to maximize the chances of fruiting at a reasonable size?

I do have a grafted LZ that could be grafted onto the seedling at some point. But right now, I’m not sure that the grafted LZ is going to survive. It’s not growing yet this spring and is very small.