Very easy, much bigger block, different intake/exhaust manifold.

Commander six:

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=2497712599&indexUR
L=9&photoDisplayType=2#ebayphotohosting

The Commander six is larger and has sort of a ram horn manifold.
Joe Roberts

The easiest way is a quick glance at the exhaust manifold. On a
Commander Six, the manifold goes up and over the intake runners; kind
of a "ram's horn" look, to quote the Chevy guys. On a Champion, the
exhaust manifold runners are  entirely under the intake manifold.

Because of this dramatic difference, you can usually tell which
engine, say, an old truck has, even in a poor or dark under-hood
photo. BP

"Robert Black" <transtar56@eastlink.ca> wrote in message news:

My favorite cue is to look at the water pump. Champion water pump is
small, and does not come above the top of the block.

Commander water pump is larger, and the pump body rises above the top
of the head.

Gord Richmond