Thanks for your thoughts and virt
@clem much appreciated. I like hearing different perspectives and ideas.
Hi Drew
Just a couple of observations. 1. There is a grafting method using chisels for older sections of trunk and branches that i prefer for a situation like yours. Essentially much of the process is the same with the exception of preparing the host cut.
Use a straight chisel to create a vertical cut lengthwise along the site to be grafted, oriented with the sap flow.
Insert a chisel approx 25-30 degree by hand in to the tree , tilt inward to the tree then use a small hammer to insert the chisel deeper creating the length of cut to insert the scion. leave the chisel in place.
2. Preparation of scion material by decandling the previous year is best and using younger scions with 1 year wood has been most successful for me. ( pictures above seemed to show the use of older material for scions.)
3. The picture below will illustrate the result, near the upper part is a completed graft that took from the previous year and subsequent grafts that have been added once it was apparrent the tree was strong enough for grafting to be successful!
Caveat, I recognize that this tree is not the advanced age shown by yours but the process is the same.