Newbee SP U33C Question

I am starting to model the Southern Pacific in the 1970s. I would like to get a Southern Pacific U33C. I know the Atlas model needs a few corrections to make it right. I read somewhere that the new (?) Altas U30C might be a better starting point. Is that true, and what are the corrections that it needs, if any? How are these Altas engines and is there better out there? Thanks.