On this picture you'll see a straight line and over at the left above the line you'll see a number 8. I marked that with a straight edge and two cross lines at exactly 8 inches. When you go to put the support back in you'll like having that there because all your original marks like spot welds, etc. will be gone.
Here are some straight edge marks. They will help you make sure that your support is in where it was before because you might have bent the metal when you broke the spot welds apart.
I'm doing more marking here. I just taped it up so you could see what I was doing with the square. This will give you the side alignment on the support. If you look real close on the very outside edge of the rocker panel you will see where that line goes right into that edge of the rocker panel. That might be the only line you'll have left on the rocker panel, although you will have the marks up on your support yet. It only takes a minute or two to mark these and you will like having them.
This is the welding helmet I bought about two years ago, I went through a few welding helmets and because this one works so good I thought I would mention it. It's a little pricey, about $225 out the door, the bride is typing this and I'm doing the talking and she stopped typing when I said $225 and looked at me and said "You gotta be kidding me" anyway its a Miller Auto-Darkening XLi and it's really light-weight. Anybody who puts 1700 sheet metal screws in a floor pan should have one.
This is the respirator I use for welding. I also run the exhaust fan with a cross ventilation. Not real breezy but the air is moving through.