Jim,
I've seen A LOT of 1980-1996 Crossmembers like that, with the cab mounts poking through the hole. I was very fortunate that these ones were all still intact, albeit a little thin. At least they were worth patching, and I think now plenty strong.
Welding overhead ugh...
Been admitted to the burn unit lately??...lol.
I did a lot of welding when I was younger, and did a lot of overhead welding with 6011 rods...I remember having burns all over my head and neck...lol. UNFUN.
PS: I'm really loving the needle scaler. I've been using it steadily on all of these parts.
Good job! Quite the project!