71 C10 Crossmember Identification Help

[AZBuckHunter]

Good morning.
I'm hoping somebody can help me identify the crossmembers in my 71.
I recently removed a 350/350 combo to do some upgrades and cleanup. I realize that was not the stock application.
As pictured below, I have labelled 4 crossmembers.

1 = Frame Brace?
2 = Engine crossmember
3 = ?
4 = TH350 transmission crossmember

My question is, does crossmember #3 need to stay or was it for a previous manual transmission? I'm hoping to just be able to grind the rivets and remove #3 while leaving the rest in place. I'm staying with a th350 transmission like I removed.

If you have a good eye, you will see #3 is torch cut on the right side rear portion where it mounts to the frame. The shift linkage for the th350 was mounted there where its cutout.

Thank you