[dsraven]

i wouldnt worry about fenders until you get the cab done. do like ogre says, poke around the roof gutter, all the way around, to see if you have any soft spots. blasting the cab will reveal any spots as well. before you go cutting anything apart i suggest to install the doors, if theyre off, and once they fit the cab then brace the door openings on the inside, like an x, and also the front area from door post to door post, then the doors can be removed and tinwork cut off as needed without worry of the cabchanging shape as you fit and weld stuff back on. if the windshield fit well you may also wanna brace the windshield opening just to be sure the windshield fits back in the hole when done repairs. that eyebrow panel is/was available and also comes with the complete roof panel. there are guys here who have replaced the roof and posted pics so you know what you are getting into before you start. I suggest to download a free copy of the 55-59 chevrolet truck factory assembly manual from the trifive site and peruse through that as it will show you where all the spot welds are located and how stuff fits together.
most of thesecabs have the rusty floors and hinge pillars because water gets trapped in the cowl plenum and drains out through the foot vents. the inner cowls have drains at the bottom but it doesn't take much to plug them at the little hole they have at the bottom. leaves, pineneedles, dirt, whatever.