Bartamos, it's all good. I did see the advice in your response, which I am taking onboard. I'm starting to formulate my strategy. The initial thoughts are that I do want a known good point as a reference or starting point. Even though the front part of the passenger side rocker panel is gone, the rear 3/4 of it is still there and in place. It seems to me that between that known point, the rear of the floor pan (which is intact) and the pinch seem between the firewall and toeboard, I should be able to figure out the proper alignment of the floor pan half. Once that is in place, I can go back and remove the rocker panel and under floor brace and then properly align those parts. From there, I would hope to figure out the alignment of the cowl parts (inner, outer and filler).
It all sounds good in my head.... But as they say, no battle plan survives first contact with the enemy.
I really liked the suggestion from Kevin about how to brace the cab. I'm going to try to do that before starting. And before bracing, I've got to develop some welding skills. So it would seem that I have some time to refine my battle plan while I practice welding on scraps.