I'm planning to use either Hairy_Hen's mixes or the GOUT audio tracks themselves, most likely the later because they are the original audio tracks.

The GOUT audio tracks are not the originals. They are the remixes made in 1993, and the first movie in particular has very significant differences in sound effects from the theatrical release. The other two were not fiddled with in this manner but are still not exactly the same.

While my versions are not the exact originals either, they approximate what was heard on 70mm prints as closely as is reasonably possible, and therefore 'feel' more like them. Also, all the GOUT tracks are reduced in level by 4 db due to DialNorm, and in ESB there is significant dynamic range compression for some reason (my theory is that it was taken from a vhs master); but the levels of my tracks are exactly the same as the laserdiscs.

Naturally, the edit would have to be GOUT-synched for them to work. If there are places where the special effects from the SE are retained, then the audio won't always match up to the image. In such cases the only decent option would be to splice in brief sections of the 1997 mix to compensate.

So for the original trilogy will it still be a lossless soundtrack, is there even a lossless for either of the Hairy_Hen's mixes or the GOUT audio tracks?

The 1993 PCM tracks have been around for a while, and hopefully my new versions will also be released available in lossless. ;)