It will depend on if it is an ACELA or a REGIONAL train or exactly what the train is that services that route!
Sometimes as far as Amtrak goes you may not know the layout until the train literally pulls into the station.
Quiet cars can be towards the front, Business Class on the Regional can be towards the rear. Cafe's are generally in the middle of the train. First Class is usually the last train on a Regional.
I generally travel the Northeast Corridor Providence to NYC and I have asked the Amtrak personnel the day I am departing what cars are where depending on the type of ticket I have purchased....Business Class as vs Coach. All Acela's are Business Class but on the Regional you pay more for Business Class and it is in the back.
I have always wished they did seat assignments. The MAD DASH to get to a seat esp at holiday time while traveling Amtrak can be cruel and abusive.