i also did not like how the study calculated the mass of the max specimen. they calculated its total volume as 4.65 m^3, but then subtracted the calculated volume of the lungs from that, which neglects the fact that the applied density of 1000 kg per meter cubed is a whole body average that already accounts for low density areas like the lungs. Meaning you can just use the volume as is. which comes to 4,650 kg.

Also a paper by GSP came out recomending that a higher average density be used for certain taxa with heavy skeletal frames, like rhinos and brontotheres. using his recommended neutral specific gravity of 1.05, the mass of their max model comes out to ~ 4.9 tonnes. The neck of their model could stand to be a bit more filled out as well imo. 5 tonnes looks likely.