Oh, you have in your picture inner rockers that tie into the floor, you will not be able to install them properly until you cut and remove the lower portion of the A pillar, then usually the lower portion of the inner kick panel is also replaced, have you looked at the condition of the front support yet?
You really need to read Rocker replacement 101 to see what is all involved in doing this, there is a link in the thread below, post 6 i think.
http://67-72chevytrucks.com/vboard/s...01#post7498530
Your more than welcome to comb thru the last 4 or so pages of my build thread, i'm just finishing up with partial floor, inner/outer rocker, inner kick panel and lower A pillar and front cab support..