There's way too much we don't know, like where exactly their muscles were, how strong/dense/fast their muscles were, the mass distribution of their internal org

There's way too much we don't know, like where exactly their muscles were, how strong/dense/fast their muscles were, the mass distribution of their internal organs, the elasticity of their tendons, how flexible their joints/spine/tail were in which directions, how elastic their skin was, the density/strength/flexibility of their bones, etc., etc. Pretty much all we have to go on is mineralised bones, which tell us quite a bit but leave out the large majority of information about them.