No. Each version can only save one version back (File>>Save with Options), so you need 7.0 and 6.1 as well.
If it's only one file, you can post it here and I'm sure someone will do it for you, but for many files you have a problem. You should also consider the fact that 7.1 has many features that weren't available in 6.0, so if you have them in the code, you will lose them in the process. In general, you should probably work with only one of the versions on a regular basis.
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