Blueranger, You might as well give up on this. These guys WANT TO WELD even if it is not technically the proper fix for this particular set of circumstances...for several reaons. They insist on using the word Pop Rivets even when someone says Rivets...They will not consult with engineers who deal with this kind of restorations or even the standard books on sheetmetal repair...
They insist on butt welding when it should be plug welding into holes punched into the new metal. Plug welding most closely reproduces the Resistance ( spot ) welds used to contruct the car in the first place...
I am only posting this for future reference in case others want to check out the reference materials already published. These guys have already made up their minds... but we tried right from the first...
They are willing to completely ignore the fact that taking the metal to welding heat... particularly where they are not protecting it from oxygen on the backside of the weld changes many important characteristics of the type metal chosen for this job by the manufacturer.

Richard, When you set your dash on fire... I told you to go get a CO2 fireextinguisher.... you really need one for the safety of the whole neighborhood.
It has to be CO2 to be practical for auto repair... you can use it a little at a time because the valve will reseal... and it does not put out a huge amount of stuff which will have to be cleaned up...

" Ships are welded not riveted together, except for a few older lake boats that haven't been scrapped."--Warren

That pretty much shows that the rivets worked.... those are the ones NOT scrapped yet... LOL