Best bet is the Academy M113A2 kit. It includes parts like the rear fuel cells and the newer type trim vane not found in the Tamiya kit. There are also the smoke grenade launchers in the Academy kit. The Tamiya kit is a straight up M113A1 and the suspension differs from the A3 with a missing shock absorber.
The laterals were replaced by a steering yoke as well. That should not be too hard to scratchbuild. I did an M113A2/A3 side-by-side comparison for the modeler who wanted to update a kit.
http://www.armorama.com/modules.php?set_albumName=albun63&op=modload&name=gallery&file=index&include=view_album.php