I have a new JHE article out on basicranial anatomy in bipedal or upright marsupials and primates! I found that although upright primates do display a more inferiorly oriented foramen magnum than other taxa, this reorientation is more closely tied to snout length than to upright posture across mammals. Free to download until October using this link.
Citation: Villamil, CI. 2017. Locomotion and basicranial anatomy in primates and marsupials. J Hum Evol 111:163-178.