Machining out the rear frame and adding ash hoppers is an upgrade to consider. Another is to turn a correct diameter stack. (stacks on Samhongsa built Williams and Weaver PRR switchers were fat in order to accommodate Seuthe smoke generators). The model below was up-detailed by my late close friend and PRR modelling mentor Ray Jury some 20 years ago. My recent upgrade was installing a Tsunami2 DCC sound decoder.