Prepared to upgrade from 1.3.7.1, nervous

I've done step 1 and most of step 2. I've found using BBedit that there are significant to minor code variations between the original 1.3.7.1 install package and the current in use zc. In the admin folder 150+ files had minor to major code differences. In the includes folder, another 250+. I have compared them all and make a complete list of all variant files as suggested.

Question...are there so many differences because my customer's site uses a template monster template? And is this amount of file differences typical or more than usual? It seems over the top in terms of an upgrade. Granted, many of the files have small differences, but I'm a functional php manipulator, not a coding master.

Also, If all goes to hell can I just upload the backup of this site and be back in business?

Please advise,
thank you

Zen Cart 1.3.7.1

Patch: 1::
Database Patch Level: 1.3.8

v1.3.7.1 [2008-11-08 16:15:41] (Fresh Installation)

Do not do this to the live site
https://www.zen-cart.com/tutorials/index.php?article=108
https://www.zen-cart.com/tutorials/index.php?article=98

If the template override system has bee adhered to then ONLY those files that are in the template_named folders need to be merged/updated
Not all the files as the core files are just replaced and if you are currently using the core file than you will use the new file
If you have a custom copy of a core file overridden then it needs to be updated

Roger that...

Still seems hairy... Will have a go at it. Customer needs multi-language capability and upgrading seems to be the best first move in this approach.

AHHH, just re-read your post and it sunk in to my thick skull! Got it, the template files that are currently over-riding the core files, where most customization and modifications have been done, are the ones i need to take note of. I re-integrate these code differences using the new core files as a base, make my changes, etc. Any modules will have to be replaced, updated, or abandoned if compatibility issues exist.

Much simpler, and much clearer,
Thanks a bunch

Got it, the template files that are currently over-riding the core files, where most customization and modifications have been done, are the ones i need to take note of.
Correct!!!

Your the MAN!!!

I feel immensely better about this now! Totally doable, thanks again!

(RoloTomasi has 4 BlackBelts in real life and looks forward to his ZenCart BB someday)