Another Outer Rocker Install question

[70Chevy4x4Nut]

I have gone through as many of the rocker install threads as I could find. I need to install both rockers and one corner. They are not too bad but just starting to rust through and I figure since I've gone this far I would do it right. Sounds like it is best to have the doors on when doing this job. I found this out after I removed both doors and fenders (cab is gutted). The original doors had been scraped on the bottom and were distorted at the bottom and were not even with the rockers. I have purchased two good used doors (original factory doors).

My questions are:
1) Do I reinstall these "new" doors and just line them up as best I can without the fenders?
2) Is the only part you are trying to check is the seam at the bottom?
3) My backing plate or inner rocker is solid. Do I need to brace the cab, or will this piece keep it from getting out of square? (the cab is still mounted to the frame)

The rockers are 95% solid, but wanted to do it right the first time. Could I get by with only a patch repair or is it better to go ahead and replace them?

This is a fantastic forum with lots of good help, Thanks ahead of time