[checkout] - template override for checkout module

I need to make a few changes to the checkout module templates and I'd like to do it via template overrides in my theme folder (as detailed here: http://codex.gallery2.org/Gallery2:Editing_Templates). Can't find the template version in checkout's module.inc, though... Is there one that i've missed, or does it not have one? And if not, does that mean all change have to be made directly to the module (i've tried using a folder called 'checkout_' without the version number but it doesn't seem to work)?

I know that this is probably all moot as modules for gallery2 are unlikely to be updated now, but it's really helpful for me to keep all my changes in one place when updating from test to live servers etc.