lower control arm placement ?

[68on22s]

I have a 1974 crossmember for my 68 and I am taking the crossmember apart for powdercoating. The lower control arm comes off with four bolts on each side. The tube that is mounted by riveted brackets on the xmember comes off and is not marked for where the tube sits for when you place it back in the bracket mounts. so I could put one the arms on in the wrong spot when I went to put the xmember back together. How can I be sure the tube is in the factory place when I get it back together. one thing to keep in mind is that I cant mark it because I am painting the arms.