Wollfen was referring to box tubing.
I've made/welded on brackets on my 68 fury (from miter-cutbox tubing), be aware wedling it isn't as easy as you'd think. In your mind you picture just getting in there and welding around the bracket, but it's actually a lot tighter in reality. I did mine when my grille/radiator support was out, so I could lean right in, and it still was a little tough to get at all the positions/angles I wanted. And I was using a fluxcore with a small 'nozzle', not a much-larger MIG handle.
It can be done, just don't go into it thinking it'll be a piece of cake.
As far as location, hang the swaybar onto the strut rods (use new bushings) and hold that up into the air with the bar-links on it, and that will help you locate the brackets also.
Make sure the boxtube is the right thickness (should be 2x the pilot height) so that both bushings 'pilot' into the hole completely. You don't want them to squirm and eventually slice thru the pilot of the bushings. you want them to pilot and smash-down, not be merely working on clampforce.
If FirmFeel sells their framelinks separately, those are a really good piece to use vs factory. But you'd need smaller bushing ID. IF you can afford a whole FF bar, so much the better! I have one and love it.