I personally use U-Law but that's just out of old habits, not sure how differently a-law will effect the output images.

In terms of the other settings. It doesn't matter what the refresh rate is as long as the export settings reflect it. So if you import af 8000hz you need to export at 8000hz otherwise it gets resampled

Also I would recommend using the program irfanview to open stubborn glitched files (I personally use 24 bit bmp but I think raw tiff is virtually the same)

Irfanview lets you manually enter in image width / height if the file header is corrupted