At two days, you can tell many breeds apart by wing feather length. Then, in those breeds, of which Marans are some, the pullets feather up faster - they get their tail and back feathers faster.
Once they're past that, you're into 'wait and see' - comb and wattle size tend to relate to how well developed they are, as well as pullet and cockerel, at the age yours are.
Yes, you can Marans as described, while they're 'in their fluff'.