Re: your rod
The Square Cube Law does not apply. You are proposing a change in only one dimension, length, when the law applies to proportional increases in all dimensions. So long as you are maintaining the same diameter, doubling a
or tripling the length will only double or triple the volume and mass.
If, however, you double your rod in both length and diameter, then the Square Cube Law DOES apply and the area of the rod would be four times greater and the volume would be eight times greater.
And therein lies your error, I believe. You have assumed that your giant dinosaur has increased in all dimensions by the same amount that its length has increased over a comparative dinosaur, correct?
As a real world example: an earthworm does gain 8 times it's weight growing from 4 to 8 inches - clearly it hasn't doubled in diameter - it has probably only marginally gained in diameter - and thus will be slightly over double the weight. It appears there must be a scale. You, it appears, are using the extreme end of the scale, which would be accurate if two dimensions (I am taking your word for this part) increased at the same rate. But according to the illustrations I have seen, that is obviously not the case. The long, thin parts are longer, but not commensurately thicker.