Are you referring to the left and right versions of this part?
I/we have used them on my 1954 Suburban.

You cut off all bad metal (at least).
Then trim the truck metal and the patch-panel metal until they match-up.

We used "CLECO" style fasteners to hold the part/parts in place - then tack-weld, etc.

Let's hope a "pro" chimes in and corrects me, and adds more/better information.

Tim
1954Advance-Design.com
1954 3106 Carryall Suburban
1954 3104 5-window pickup w/Hydra-Matic
The 216 and early 235 engines are not "splash oilers" -- this is a splash oiler.