On my 52, I went rockers first, then floor & suppports, toe & cowl, and finsihed with cab corners. With everything cutaway, I used 2x4s bolted to the firewall and resting on the frame to support the cab.
Before you cut, measure everything and write it down. I screwed up, got my floor pans too far forward by 1/4" - 1/2", and in turn, the trans cover didn't fit right and the clutch arm hit the toe/floor joint. Nothing shears and a hammer couldn't fix, but it would have been easier to do it right. Good thing it's not for show.
http://www.homestead.com/chuckthetruck/page3.html
