The only other piece of advice I have is take off the gutter before you trim it back. The gutter over the doors is spot welded in from the underside of the sill and if you drill out the spot welds it can easily be removed. This creates a cleaner and less cluttered process, now all you have is 2 pieces of metal to weld together instead of 3. Also if you don’t cut the gutter off the little piece of metal that is left to weld to the roof has rusts underneath it and the rust will eek through your welds if you don’t remove it. Don’t forget to replace the gutter material with a wider and new piece of metal after you spray it with weld through primer to fill in the gap that is left. I also think some small round stock could be used to fill in the gap and help create a lip to keep water form coming into the cab.
Her are some links to other posts about the subject and a few pictures I "borrowed" from another member:
http://67-72chevytrucks.com/vboard/s...d.php?t=450753
http://67-72chevytrucks.com/vboard/s...d.php?t=354144
http://67-72chevytrucks.com/vboard/s...d.php?t=389735