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Actually I have made some progress overriding/modifying themes in PFv4. It's taken me some time to get used to the new layout, but so far good.
I found a fix (sort of) for thumbnail cropping problem in the Material Theme. Using the Inspect tool in my browser (I use Chrome) I identified where in the bootstrap.css file the code is for each of the photo thumbnail containers (i.e., Album Covers, Photos, Photos in the activity feed, etc.). I then changed the background-size from "center" to "contain" and I added a background-color, in this case black (#000000). It's not the perfect solution, but it looks much much better then have heads cut off.
Some of the differences are pretty extensive. I don't think I'm good enough to modify the v3 files using the v4 files. I'm going to try a different track. It seems to me that the problem is that the page isn't sending google the api key. So I'm going to find out where the code to call the map is and hard code the api call.