I think that first you need to identify those companies that will support your vehicle, by support I mean they make the pieces you need. Companies that you'll hear about are Heidts / Fatman / Kugal and there are others.

You'll need to gather all the frame dimensions and the locations of supporting components. Since the car has had 3 front suspension, you'll need to ensure that the front wheels end up in the location that you need / want them to!

Having the column or headers on hand right now is kind of secondary, you'll need to have an idea of where you want or need these components to land but right now you need to get the car apart, up on stands and gather the measurements, you need to verify where the new components will mount and the quality of those materials.

In your pictures the front wheel look centered in the wheel openings, if they are and that's acceptable you, then you can use the the spindle center line as a measure to meet. Just like working with a carpenter, measure twice and cut once!

Hope it helps.