Deepest reach welding vise grips?

I have those too.
I got 2 pair of 18 inch ones today at Farm and fleet... ("Milwaukee" brand) not 18" reach/ also just ordered a pair of "24" ones from amazon... again not 24" reach/ only (something like) 15-3/4 I believe they said. I just ground off/ drilled out 66 pop rivets covered by bondo on my truck cab back wall. They overlapped ~1-1/2" - 2" and I'm wanting to "pinch" the overlapped area to squeeze the overhang as tight to the original as possible and skip weld that seam/ I may do the whole overlap on inside and outside of cab.... as well as filling in 87 holes... 66 pop rivets plus 21 "bondo tooth" holes. I know it'll be a "spot" weld at a time. I do have some pretty heavy copper bars I can clamp as a backup bar... if I can get something deep enough to reach the cab floor.... as far as Cleco's
there's 3/4-1" left in the overlapped panel to the outside of the Cleco's... they're not right on the edge. If I had some help holding a dolly on the opposite side of the cab wall I could try to hammer the gap shut. Were not talking much.. 1/16-1/8" or so in spots.... but I dont want to just "Bondo" that as the last guy who worked on this thing, did.
I ground off lots of bondo with a Milwaukee grinder and wire wheel.... and dont want to put it back any more than I absolutely have to.
Honestly I wish I could fill the seam with lead.... but I dont know anyone near me that could give me a "tutorial".... or else braze it in. something that will seal and not absorb moisture as bondo is famous for... I met Gene Winfield once.... unfortunately hes gone now and even if not California is a bit far from me....
It would be nice if the idiot on Marketplace that I was talking to last week, would have called me as he claimed he would.... I'd have a different cab that doesn't have this issue
Problem is most I see are worse than what I have for crazy money, would need more work than my current one does.... this one I found on MP (out of state but not crazily so) is supposed to be nice and not need anything my current one does....
Self tapping screws will do the job as well. You can put them in, tap or press the high spots between down and weld away. Same thing when you remove the screws after. Done for floor pans all the time.