A more wide-angle photo of the LZ tree you have would be helpful as well as the rootstock tree you plan to graft it onto. The LZ scion you previously posted is not yet ready for harvest. Best to wait or order some scions from Alex at Tropical Acres Farms. I just Grafted (15) scions I purchased from Alex last week to some of my older mango seedling trees and others I am partially top working.
If I could go back in time and do this whole mango thing over again I would likely purchase 20-30 poly seeds from Florida, germinate them all, and put the best ones in 5-gallon pots to grow over the next year to year and a half. After one year+ I would move the best growing specimens into larger seven-gallon pots for further root development and observation. After two years+ take the top 25-30% of the seeds you germinated and plant them in the ground with sandy soil. That's just my take if I had more time and could start from scratch. I would grow seeds like Cac, Sweet Tart, Lemon Zest, OS, Fruit Punch, Seacrest, or any other faster and more vigorous variety preferably Poly. I would also observe if the young tees have a tendency to flower very young, if so then these would likely not be the ones I would pick to put in the ground as I prefer strong vegetative growth for the first four years if possible to maximize canopy development. Being able to hand select strong growing mango seedling trees will prove to be a huge advantage long term.
Good Luck
Johnny