Off the top of my head, the three items that stand out as needing attention are the following:
1, Domes are incorrect, should be Budd type (rounded) vs, P-S (which the Bluebird did add later, but only one). Actually, maybe by mistake, the dome is a pretty good version of the P-S add on.
2, The observation car roof end is not correct. The end light should be raised and not recessed and the roof panels were very visible, not smooth like in the model.
3, Ride height seems even higher than other passenger cars, might be due to color scheme.
4, The dome on the observation is in the wrong location.
5, It may be just me, but it looks like the domes also fit poorly.