Rootstock dimension for mango grafting?

I am planning to get some scionwood from my brother sooner or later within the subsequent month or so (from the tree mentioned on this different thread), and I’ve two completely different seedlings in my greenhouse that I might probably use as rootstock, however would favor to make use of the smaller one, which is the seedling of the tree I will be grafting. Here is what it seems like now:

I do not know if that seedling (about 7 months previous, stunted from a winter in a cool greenhouse) is simply too small for profitable grafting, although. I do know there are some grafting strategies (Z graft, for instance) that can be utilized when a rootstock is thinner than the scionwood, however I am unsure if these work properly with mangos.

My different possibility to make use of as rootstock is a two year-old Ataulfo seedling that I’ve planted within the floor within the greenhouse, however I type of wish to develop that one out, despite the fact that it is a significantly better dimension for matching scionwood. Here is what that appears like:

Is there any method to make use of the little seedling with out ready for it to develop extra first, or ought to I follow the bigger one as an alternative?

I am sorry if this has been mentioned on right here already, I attempted to make use of the search characteristic and could not discover any on-point discussions.