Bending a flat does not require much of a press... BUT ... pressing out a barrel will require more room then you will have with anything smaller then a 12-ton press! Look at this tutorial (which I need to get working on again) and you will see that I am using a 12-ton press:
http://quarterbore.com/images/amdbuild7/
In that tutorial is this image of the AMD-65 barre getting pressed back in... note the AMD-65 barrel is shorter then most AK barrels!
I don't see a good picture of me pressing out the barrel especially with it in the trunion as when I needed to adjust my headspace but that required the bottom or the press to be lowered even more then in the picture above. I do not believe you can use anything smaller then the 12-ton "A" frame press but I like the extra room the H-press gives.
As an aside, I actually just purchased a 20-ton press as I was not happy with the flexing that I get with the 12-ton press when I am trying to press out tough barrel pins or when I am trying to press in a barrel. I have yet to use the 20-ton press but with the 12-ton press I have had problems keeping everything straight. I understand the 20-ton doesn't do this so I bought a bigger press.