4-bar / back half the HemiDenny / HDK way

Are my eyes deceiving me or is there a slight bend in that tube? I tacked in one side of my 2x3 frame connectors but I have 10' of 1-5/8 .120 that I was thinking of using instead.
good eye...on this one, the 1-5/8 did get a slight bed on each side...as I remember, it was two-fold, floor clearance and to make it possible to tigg the very upper areas