Here's what I did, I used my die grinder with a small wire wheel, very stiff, and cleaned the debri and rust, I hadn't done much on this photo. but I worked in the middle of the firewall from the access hole plate. I then placed a length of 1/16" tig rod in the V of the seam to be welded. Then came back and migged it together. Of course there are some areas that I won't be able to do this. I am geared up very well, respirator, goggles, hearing protection, and a ventilator to suck out the nasty air.
ON the engine side, I used my sawall to cut the ridge off, the used my angle grinder to get the remaining ridge down. This worked very well and I didn't blow near as many holes. Now the battery end of the ridge is going to require replacing some metal, but I think I should finish this today. I sitll haven't welded the metal coming down to the seam, I may just cheat and spray rust encapsulator, then epoxy primer, and filler. or maybe possibly jb weld.
