Offset leaf spring install ?

Well, your concerns made me giggle this morning. There honest.
I would not worry a bit. When you go to weld on the rear, tach it down first (of course) and then after you clean it up and cool it down, just run a bead on one side quick. Then repeat, clean up, leet it cool for a minute, coffee/beer/bathroom break.... Finish the other side. It's not going to get hot enough to like the oil up. It may smoke a bit though.

I'd leave it all bolted together