The Amtrak E60's were originally built in two versions: some with HEP, some with steam generators for 'heritage' stock, especially through trains to/from "the South". The plan was for the latter to be gradually converted to HEP as steam heat was "phased out" [ pun intended ].
I think the "large fuel tank" captures the look of either version rather well, generally speaking.
Best rgds, SZ