Floor support question

[1971K5Blazer]

So I'm trying to get my repop front floor support in and I'm wondering if it's supposed to sit directly on the torsion box or not. See pictures below. If I push the top of the support down against the frame it pulls it up at the torsion box (second picture). I want to make sure I get this right so any suggestions would be appreciated. Also, what is the small tab on the torsion box for? (just to the right of the support in first picture) Should the support go behind or in front of it? Thanks!