Rootstock dimension for mango grafting?

I am planning to get some scionwood from my brother in some unspecified time in the future within the subsequent month or so (from the tree mentioned on this different thread), and I’ve two totally different seedlings in my greenhouse that I might doubtlessly 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 appears like now:

I do not know if that seedling (about 7 months outdated, stunted from a winter in a cool greenhouse) is simply too small for profitable grafting, although.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

My different choice 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 form of wish to develop that one out, though it is a significantly better dimension for matching scionwood. Here is what that appears like:

Is there any manner 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.