Jeff Lincoln wrote:
 > what is the best way to get all of the old coolant out

Remove the pushrod tin.  Right between the pushrod tubes, on each head,
are drain plugs.  While you have the tin off you "Might" consider using
a hole saw to make access holes right below those plugs so you don't
have to remove the tin in the future.

With the radiator hoses removed, the radiator should drain.  You can
make sure by cracking the bleeder bolt (if stock) or removing it if it
doesn't have the groove up the side of the threads.

Flushing and back flushing the system helps to rid the old coolant, too.

Mike