Board Thread:Warhammer 40k General Discussion/@comment-4851119-20140118095944/@comment-74.128.152.190-20140119193731

I don't remember reading anything about Space Marine implants that states upon implantation the initiate takes on a cloned appearance of their parent Primarch. Obviously due to variations they take on certain traits, such as the pale skin of the RG, but by no means does it make them appear exactly like their Primarch.

You have to remember that these were ordinary human beings (with traits from their bilogical father AND mother) that received genetic material to turn them into Astartes from a single XY genetic source.

Unless they were vat grown from scratch each Astartes regardless of their parent Primarch will look different in some way, some differences, obviously, will be more subtle then others.

That being said, if the Emperor wanted the Ultramarines to take on the remaining members of the forgotten legions Guilliman, of ALL the Primarchs, wouldn't refuse him.