The machine with the spikes was vibrating the ballast to pack it in. The one with the plows was shaping the ballast. Often on the NS the one with the plows has a giant brush on the front that brushes the ballast in between the rails.
Here are some pics of NS equipment. Take a look at the track equipment:
http://trackgang.railfan.net/images/ns-mw/ns-mw.html
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