>>118351028a human head weighs that much because it's full of brain, which in humans is about 1.03; then there's blood and other tissues (again, these mostly have specific gravities of about 1, and are all at a single atmosphere of pressure, meaning they weigh about the same as the amount of water they would displace if submerged - less any sinus cavities etc)
in humans, skeletal weight is about 14% of total weight, but the skull accounts for about a quarter of the weight of the head, with about a third of that total weight taken up by the brain
with a t-rex we're talking about a dino that had a relatively large brain (to do a lot of scent and visual processing, most likely) but also had very much larger teeth than a human as a proportion of skull volume, and a jawline and snout adapted to match the need for these large teeth, which means that the brain as an overall proportion of head mass is probably lower than in humans
we do know that fossil bone has a much higher specific gravity than recent or living bone, because it is so heavily mineralized, so we can say for certain that a fossil t-rex skull weighs a lot more than a fresh t-rex skull, even if the fresh skull has soft tissues intact; the likely weight is hard to guess at without more data on that particular specimen (especially as large dinosaurs had adaptations of the spongy bone interior, the trabecular bone, which allowed them to grow massive without having extremely massive bones for their size compared to a human or elephant), but it's nowhere close to a metric ton, let alone the 2,500 pounds/1.1 tons that the fossil OP draws comparison with
I would guess it tops out around 600kg - just because there's so much void inside the mouth cavity, and it has such large sinuses for smelling stuff with
still a ridiculous clown amount to say anybody could lift, but there you go
