That's a common place for them to crack. (Probably right at #6... right?)
I'm sure that others will jump in with suggestions, but when you get it welded, bolt it to an old head (preferably) or a stiff piece of metal stock. Otherwise it will warp, due to the uneven heating and cooling during the welding process.
You can also look inside the ports and see where the restrictions are. You can grind away a great deal of those restrictions, but be careful. You can compromise the welds where the pipes are joined. (Others just have the welds reinforced, and then grind away
all of the restriction.)
Edit - Make sure that your exhaust system is not placing a lot of strain on your manifolds. You should at least have a hanger or springs on the left corner, where the pipe turns towards the cat. Also be careful of rain water spilling onto a hot exhaust. GM removed the weather seal at the front edge of the decklid (most of them, anyway) during one of the recalls.
[This message has been edited by Raydar (edited 01-23-2022).]