I can't speak to 39 but on my 38 the welting is only between the fender and the body, including the radiator shell. On the 38 there was a foam like material between the fender and the running boards and between the fender and the firewall. Between the running board and the body is a rubber strip that's sold by everybody.
I have a welting installation trick that made installation much easier. Take 1 inch wide masking tape and pull off 6 inch strip. Put the 6 inch strip on the inside edge of the welting, fold it onto itself so the tape leaves a 2 inch tab hanging off the inside edge of the welting with 1 inch on top and bottom of the welting. Do this at intervals along the welting. When you get the fender mounted, use these masking tape tabs to pull the welting tight as you tighten the bolts holding the fender to the body.
Brian
