If you're bored, here's a really extensive list of different types of animals' weights and their organ weights: https://dspace.lib.ohio-state.edu/dspace/bitstream/handle/1811/3110/V40N05_219.pdf?sequence=1

Agree with Nance, fat is stored not only under the skin (above muscle) but also around the organs. So individual size, I am not sure, but the entire internal organ system composition would be larger given the fat surrounding.