Hi Chuck, I am no expert on the subject but being that my fenders and cowl are off the truck truck right now for a little repair and repaint, I might be able to help.
http://rides.webshots.com/photo/2930994000083734483ttFpuW The inner and outer fenders do go on and off as one. You will definitley need a helping hand to put the whole assmbley back on the truck. When I get the parts back, hopefully next weekend, I can take some better shots of the bolts that hold the two together, and which holes are used to attach to the truck. You ought to be able to figure out from the cowl fender support a mounting hole pattern and mach those up to the holes in the fender. I put the cowl on first. I plan on getting the fenders on loosly and then slipping the welt in, after some strategic trimming around the bolts, before tightening. I only used the welt between the cowl and the front of the fender when I originally asembeld the truck and that was a mistake. The paint on the cab was a little beat up from the parts rubbing together. I may even use it between the steps too this time.
Billy