Well, if the site is 1.5.5a and not 1.3.8, then the first link provided will be of little to no value.

If operating under ZC 1.5.5a and php has been upgraded to 5.3, there should be little that would need changing as I can recall other than addressing the issues that were identified in the 1.5.5 known problems thread: https://www.zen-cart.com/showthread....24#post1306424

1.5.5 was designed to operate using as low as 5.2.17 (which sounds like was the case).

As to the "age" of the store assuming that the 1.5.5a files were fully put in place, is yes a little old, but no where near what is often seen.