This is for the purposes of testing only. Correct?

Yes.

Within your test script, load the ASCII and pack it using the various "Native format" specifiers.

That's a very elegant solution indeed. However, I assume GrandFather is correct in his assumption that the SOL files are little-endian regardless of platform.

If one uses "Native format" specifiers to create the test files, one would get big-endian test files on big-endian platforms. The tests would then no longer reflect real use of the module on those platforms.