For such an iconic Triassic archosaur, Postosuchus has proven lots of trouble when it comes to restoring what it looked like and how it got around. Getting the proportions right isn't a trivial matter, as none of the remains are so completely preserved/prepped/described that they can stand in for an entire skeleton. Simple cross-scaling of the specimens isn't possible, as they are of different sizes and exhibit allometric scaling (more on that in a sec).
With a bit of care I've managed to pull together a reasonable composite based on (and scaled to the size of) the type specimen, TTU-P 9000. One of the larger sticking points (in part related to getting the proportions correct) has been if and to what degree Postosuchus was bipedal. While the forelimbs are robust for their size, recent work has noted that the forelimbs are substantially shorter than the hind limbs, which at least in the type specimen I heartily agree with.
One thing that is interesting, however, is that the smaller paratype specimen TTU-P 9002 has different limb proportions - the forelimbs are quite a bit longer relative to the hind legs, and in fact are nearly as long as in the substantially larger type specimen. I've scaled down the skull and axial skeleton to match the limbs of 9002 in the smaller skeletal above. It's tempting to infer that the young of Postosuchus were quadrupeds (or at least were _more_ quadrupedal), and as they grew Postosuchus spend more time on its hind legs alone.