The <1/2" hole in the Chevelle’s frame behind the front driver’s wheel (where these always rust, there’s a seam here) turned out to have been known to someone in the past, who put some sort of metal putty in/on it to hide and/or “fix” it.
When I attempted to clean up the area for welding, I discovered that the area around the hole (which appeared while stripping undercoating from the frame) was very brittle epoxy or all-metal filler or such. I removed that and cleaned up the area to discover a significant structural deficiency.
This piece is very well into solid metal, and will give a solid base for the main patch to connect to so that it ties the rail into the front section. I need to buy material for that main patch tomorrow.
While a bummer, it’s not too crazy and should be ready for paint (and plenty of fluid film on the inside!) by the weekend. Once plated, I’m tempted to tear into the bottom part of this seam to make sure it’s not in need (or soon to be in need) of repair as well; but it’s probably fine since the front end didn’t fall off the car with this whole area missing.