... have hit a wall with printing custom print sizes from Aperture 2. Any other sources of info on the subject would also be appreciated.
Have you taken a look at Aperture 3? Here's a list of printing improvements:http://www.apple.com/aperture/features/#printing
The User's Manual is on-line (in case you haven't looked):http://documentation.apple.com/en/aperture/usermanual
Just trying to help. No fun to have a wall keep you from completing what you set out to do.