Quick thought: each byte is a printable ascii character between space (0x20) and 'Z' (0x5a) inclusive. All these bytes appear in all the encoded files. Does anything interesting happen if you interpret the files as encoded in base 59?
(Edit: obviously I'm talking about the files after they have been base64 decoded…)
(Edit: obviously I'm talking about the files after they have been base64 decoded…)