Mike, Those little stick outs are little stake pockets. The top one originally had a hole on the bent,angled top side for a hole but now it's closed on mine. The one underneath the rear fender is only a side panel stiffener. It's a stake pocket that I cut on angle to reproduce the original one.
The bottoms lip kick out on my panels are 3/4", but there's room for up to 1". My panel sides, I tried to cut to 18 3/4" and it came out at 18 7/8" which seems perfect. I'm not sure how these pictures turned out but here is the diagram I drew before I got it bent.
The top side (the bent part) I cut at 4 3/"4 but I ended up trimming off 11/16" in order to have a nice gap to weld on.
1970 Chevrolet C10 Grandpa's -- My first truck -- In progress to shiny Follow the build in the Project Journal 1950 Chevrolet 1-Ton Dually "Ole Red Girl" In the Stovebolt Gallery More pictures here 1951 GMC 9430 1 ton dually--Shiny! | 1972 Chevrolet C20- Rusty- the puzzle box lid for the C10 | 1962 AMC Rambler American- my wife's Parts trucks- 1951 GMC 9300 | 1951-GMC 9430 | 1951- Chevrolet 1300