If the metal above the pinch weld is ok, you can cut out the lower piece, then that gives access to the spot weld on the pinch flange.
Use a hi quality spot weld cutter. I drill the center of the weld w/ a 1/8" drill. This gives a locator hole for the guide pin on the cutter.
You can also grind the welds real thin, then split it open w/ a weld cutter tool. Once you have the old metal off, you can grind the scabs off. The 1/8" guide hole will fill back in when you spot weld.
I use a 3/16" sheetmetal punch to put the weld holes in the new pan.
Locate the pans, use self drilling, small screws to hold in place, several vicegrips to pull the seams tite.
If you want more info, give me a shout..
706-342-3152 H/S
770-265-5144 C