Paddy, how big are your "other chunks?"  Why do you want them squared? 
How straight is the grain on your chunks?  The answers to size and
straightness of grain will determine the tool(s) to use. If the grain is
straight you can roughly square shortish pieces by splitting -- wedge
and sledge work. Smooth and shape it after.  Here's a video of my friend
Anton working the side of a beam with a Russian ax.  How proficient are
you with axes and hatchets?  There are tricks in using them.  Anton's ax
is sharpened to about a 20 degree angle, basically chisel sharp. 

https://www.facebook.com/1657035445/videos/pcb.10225471645972190/145690434473354
0

https://www.facebook.com/1657035445/videos/pcb.10225471645972190/560828602491851


If you aren't proficient with axes, aren't familiar with using an adz,
practice first.  Neither one is just a chopping tool.  Axes can be used
in a slightly slicing motion for shaping.  The adz is a bit more
difficult to explain. 

Mike in Woodland 

I've had a largish Russian olive tree removed from my front yard - it's
chief offense being an uninvited guest in my clay sewer line. I've saved
some significant branches and intend to make them into various rustic
projects. The crew was very kind in creating somewhat of a face with a
chainsaw, but I am looking to neander my way to squaring up other
chunks.

Do any of you woodspeople have a favorite hewing tool, and almost as
importantly, is anyone willing to part with one or direct me to a
source?

Best,
Paddy