Certified GKH Gardening Expert
Grafting requires quite a bit of practice and patience. Be sure that you have a tree that you can take between 10 and 20 branch tips for grafting, and that many rootstock trees also. This will guarantee you at least one or a few depending on your skill level with the task.
Grafting will be done during dormancy, or late Autumn, usually, but can be done in early spring, too.
These articles will help: https://www.gardeningknowhow.com/ornamental/trees/tgen/grafting-trees-what-is-tree-grafting.htm
With Apricots, it will probably not do very well in such shallow soils, Though if there is plenty of room between the blocks, and soil under it then you may still be able to plant there. It can't hurt to try.
Here is an article that will help you to grow Apricot trees: https://www.gardeningknowhow.com/edible/fruits/apricots/apricot-tree-growing.htm