For the nomenclatures, see mustangman’s post.
And yeah, this’ll take welding. You won’t find the individual body piece on the market, because they’re not sold that way. The problem is that unless whoever does the work REALLY knows what they’re doing, and preferably has an alignment table, there are extremely likely to be serious chassis alignment issues once the new piece is welded in. Normally when a piece of sheetmetal is cut off and a new one welded in, framework has to be tacked to the sheetmetal to hold the parts from moving around or they’ll never align properly again. In addition, sheetmetal distorts and contorts when welded. A good welder will tack the parts together and them weld in short spaced welds to help mitigate this, but it’ll take a good welder. In body parts you can often get away with it because slight misalignment doesn’t affect vehicle operation, but in your case you’re talking about something that does, and also something that will be subject to serious stresses. In your case whoever is trying to weld the new piece in has nothing to properly align it to, and absolutely must know how to weld properly… I’d also put gusset plates in.
Having said that, I’m having a hard time ascertaining from the photos whether it’s the actual tower that needs replacing. In the first photo I see the top of the strut, and it appears to be mounted in the tower. It may be that the structural piece between the tower and the radiator support area is what really needs replacing. That’ll still take someone who knows what they’re doing, and it’ll still need to help support mechanical components, but alignment might not be quite as critical.
Excellent photos and description, by the way. I wish everybody would make the effort.