1980 C10 - replacing edge of floor and inner rocker without cutting outer rocker

[skyphix]

Hey All,
I am about to start digging into the body work of my project truck, and I've never done this level of body work before so I figured I'd ask. All the videos and info I have found involved replacing the outer rocker because its also rusted... in my case, my outer rocker is completely solid (maybe not on the inside, I guess,) but the outer edge of my passenger side floor is rusted through and it has started into the top half of the inner rocker panel.

It looks to me on this diagram



That part number 1 in the diagram, the edge marked as measured 17" would fix my issue if I cut about 4" into the flat part of the floor pan and welded all of that in. I have good weldable material toward the bottom edge of the inner rocker panel and as I said the outer rocker is good.

Do I need to cut out and thus, replace, my outer rocker as well, or can I cut the floor and inner rocker out of the way just shy of the pinch weld at the bottom and slip it in, clamp, and weld it? Or is it just worth it to cut the outer rocker and either re-weld in the old rocker or just replace it with a new rocker?

Thanks - I suspect I'll have quite a few more body work questions as time goes on, but this is my most complex rust issue to deal with, so it already makes my trip to SC worth it (I wouldn't have ANY metal to work with at the price I paid for this truck if it had been a Maine truck its whole life.)

EDIT: In actuality, it looks like what I thought was the inner rocker, isn't... its just part of the floor.