Does high G actually cause a higher or lower blood pressure at heart level? (search engines fail to give an answer) I think the problem there is blood packing to the lower body, and a sauropod would have enough blood and strong enough veins to be able to hold its head upright.

It's not really obvious to me why the sauropod heart->head->heart loop shouldn't be considered as a "siphon". For all the blood that's going up there should be an equal amount of blood going down.