If that were my truck, I would go ahead and cut out the front support and get a replacement. It looks pretty sketchy, especially where the rocker panel has rusted away in front of the door pillar. You're going to need to replace the rocker panel, or at least the front section of it. I had the same condition and opted to replace the entire rocker on both sides. The other consideration is that you can't really get good welds on rusty metal and will need to grind away the rusty stuff, possibly resulting in some weakened metal as it gets thinner. You can use the hinge bolt locations to establish the correct distance between door pillars (dimensions available in the FAM.) Looks like you've braced the door frame pretty well.
