1) i used double sided tape to hold on and fill in the blank spots. it is anti squeak and water sealing.
2) is a little tricky to make it look good. i filled the U with glue/caulk and taped it tight. once installed i pushed it back into the body, used a lot of tape to keep it clamped. i shaved the firewall standing seam, i left enough to fill the inny on the inner fender
3) bad pic but i glued it to the fender, it's obvious where it goes. if you still have your fender on you can probably stick it in the gap at the hinge end. zoom in on the pic., inside of my fender and inner fender and bottom of cab has rhino liner bedliner on it
58-9 inner fender goes on before fender, i believe 55-7 can go on before or after fender