[mr48chev]

You will have to melt the lead out and clean the area up before you can weld it. My guess is that that area has been repaired at least twice, once with lead and later with plastic filler after the same spot was dinged again. Lead done right will flex some with the steel it is on .
The hacks used to suggest leaving the holes in the sheet metal for the plastic body filler to squeeze though for what they said was a better attachment to the metal but all that does is let moisture get behind the filler from behind and cause it to rust behind the filler. My old cab is a prime example of that as I didn't have the patience to take my time and do things right back in 1980 when I chopped it and now taking those short cuts shows.

If you pull the dent don't use one of those drill the holes and stick the screw in dent pullers, that is worse than leaving what dent there is and putting filler back over it. Eastwood sells a dent puller that you weld a pin to the metal with your mig welder to use with the dent puller and then cut the pin off flush that works pretty well. i have one that will get a lot of use on my Model A.

I'd still figure out how to work the dent out as best I could then use a bare minimum of filler to slick it off.