Install Stock By Attribute over Google Checkout

I have recently installed ZenCart 1.3.9h and added the Google Checkout module to it. I would now like to install the Stock By Attribute add on but notice that it hits some of the same files. Does anyone have an idiots guide to installing these two mods in that order? Or better still is there a version of the modified files available which contains both these mods playing nicely together? :hug:

TIA

By the way I am using the Classic template and here some more technical stuff:
Server Information
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I would now like to install the Stock By Attribute add on but notice that it hits some of the same files
One must include/merge the specific customizations into one file

Beyond compare or winmerge are tools that can assist

Thanks Kobra, what I was really hoping for was a list of the modifications I am required to make in each file to install "Stock By Attribute" manually.
The GoogleCheckout installation instructions do have a step by step version, for those with other modules already installed, so what I may do is copy over all the files for the "Stock By Attribute" modification and then follow the Google Checkout step by step code updates to manually re-apply the necessary changes to put Google Checkout back.
I just figured somebody may have a step by step manual version of the "Stock By Attribute" install I could follow, or even a version of the files affected which contained both the "Stock By Attribute" and "Google Checkout" code, that I could just copy over.
I will take a look at the two utilities you suggested, as there titles suggest they may be just what I'm looking for :o)

even a version of the files affected which contained both the "Stock By Attribute" and "Google Checkout" code
I think you will fing that with the number of add ons available, that you will not find precise edits to do this & that
As one can select their own set of modules that they want, it becomes up to them to "merge" the altered code pieces into one file when, as you found, the same files are affected