I have a bunch of grapes that I planted this winter and one (a Thompson Seedless) that I planted last fall.

I just finished making an arch for the thompson seedless and want to train it up the arch, but right now it has been growing quite fast in every direction. Is it too late for me to prune it to just 2 main branches that will go over the arch? or should I wait untill next winter? The plant is about 3-4 ft tall and quite bushy

Also it would be nice if I could find some resource on how to train a grape plant over an arch. This is an arch made of bent rebar similar to this:

http://www.rd.com/84791/article84791.html

I'm finding lots of info on how to train grapes on vertical posts and horizontal wires, but nothing specific about arches.