Thanks everybody for the encouraging responses. I used a cleft graft for the graft because it's worked well for me in the past. I am very successful in grafting just about anything but, for reasons I don't understand, budding have always been much more difficult for me so I typically just avoid budding (even for citrus). The graft is made about 8" above soil level, I believe (was done when a potted BT was in my greenhouse for about 3-4 weeks, waiting until it was showing some growth before making the graft). The biggest thing with grafting is to make sure the cambium layers are aligned and, since bark thickness may be different on rootstock than scion, I suspect some people may make a mistake by aligning the outer bark surface. I wrap the scion with Parafilm (BuddyTape, actually), use a grafting rubber for the union (cut rubber band would be fine), and then wrap the scion with more Parafilm. If weeping of the union is excessive, I will sometimes make diagonal cuts in different areas a few inches below the union to slow that down since I suspect excessive sap/latex may inhibit healing of the graft union. I don't think I'm as good as a grafter as Grasa has become! Still no success in root grafts for me.
I don't believe it's been talked about much lately but years ago in the infancy of this forum it was commonly said that Black Madeira was difficult to root. I've not investigated the root system of other Black Madeira trees I have growing but this background lead me to believe it was worth trying other rootstock for Black Madeira.
Suckering has not been a significant issue. I trimmed off some growth emerging from the trunk below the graft union a couple of months ago and all of the growth in the photo is from the Black Madeira. I believe I pretty much had this tree pruned to a 15" single trunk at the beginning of the year since I wanted new growth to be able to train on the same wire supporting my drip line. So pretty much 4'-6' of growth on several branches this year.
Aaron, the soil is not very dry but the soil does crack near the surface a lot because of clay and silt content. Water table is at about 3'-4' right now and will raise during the winter months, thus planting the trees on a berm. The trees are irrigated with drip. I had been running drip for just an hour or so about once a week figuring roots will go down to lower moisture but have been running drip much longer lately in hopes that will speed up fruit ripening on the last of my fruit. A recent soil test also revealed I have some sodium in the soil so I'm trying to leach that away from the trees (source of sodium is unknown, was a bit of a surprise). I also discovered potassium level is very low and that will be addressed with potash and I'll apply gypsum as well to help deal with sodium. I'm not set up at present to fertigate this orchard but may change that next spring.