At first I thought that you would tie them together, like some "fusion" project to make a massive trunk. Actually, I'm pretty sure most, if not all of them will take.
PS : I'm not sure we are in the same climate zone : why don't you specify a nearby big city in your profile (I live near Orléans, USDA zone 8a, rapidly becoming 8b).
I mean, the seasons are not exactly the same in Burgos, Almeria or Santander...
a little village between Madrid and Toledo
Can maples survive where you live ?
I have a few dozens that I'll have to give up, 1-2 yuear-old seedlings, if you're interested, I can send you some in the spring : bare-rooted, for shipping potted ones -even in plastic pots- can be expensive.
I'll post an "offer" later for those in Europe who may be interested. I'll just ask for the postage price and 1 or 2 €uros for the plastic wrap. To be disposed of in the yellow bin afterwards
I would have made a more diagonal cut though, and wire the new leader in the popposite direction: Right -> Left, instead of L ->R. I think this way you can make it vertical more easily.
How are your cuttings doing? Any take?