I'd love some corkscrew willow cuttings, but we'll be frozen in for a couple more months here in northern MN. I have some perennials at my old place - phlox in purples and some whites, dark blue flag iris, lots more that I can't think of off-hand. If you'd like to try for a later trade, please let me know. We've been moved to the "new" house 2 1/2 years now, it is time to finish moving my 25-year plant collection this summer. Oh, I should have some purple smoke bush cuttings available.

Can not see rest of documents but your tree appears to have an old injury which has became covered with bark. If you look at the tree the bark in that area and in a fan shaped portion on the left limb is different from the rest of the bark. The different shaped, coarser, bark has covered the old wound. When I planted my corkscrew I was told that this type of tree only lives 15-20 years. Start trying to root some of the branches as a replacement. The tree has compensated for the damage and it may be time to think of replacement. Only an arborist could tell you if the cost of trying to save the tree would be worth it.

Grows a bigger, heavier top that those other two (although I once measured a French pink here that as I recall had a trunk 11' around) so it might be more likely to go over for that reason. But you see big ones out in the open east of the mountains here, where they have continental conditions (USDA 4-6 or 7). Planting in a damp place might make toppling more likely as well. But as with planting of all trees and shrubs, the most critical factor could be making sure these don't go into your site with deformed (circling, knotted etc.) roots on which the trees will pivot over once the tops get heavy enough.

All that usual stuff about topping and not pruning doesn't always apply to willows, particularly twisted willow which looks much better as a multi-stemmed variety, stooled back like a cotinus or a buddleja. They are vigorous and will appreciate a cutback and continued watering. Certainly in the UK, this would be a good time to cut it back - maybe a month late but still. Your other option, to contain the exuberant growth is to keep the height and encourage it to fountain outwards - a low tuteur or timber tree guard can be quite useful for this. So, I guess you need to scrutinise the space and look at general proportions in order to plan for its ultimate growth habit - in willow, growth really follows the knife so you will need to be circumspect with an idea of shape and style.