Seeing as you've put so much time and effort into this project, it would be a shame to see the finish come out anything less than pristine. You said you were using 600 grit sand paper... were you using that on a sanding block? I know I've got small pieces of it, but you may want to have a look around for some 2000 grit sandpaper. Its approximate abrasive equal would be a brown paper bag. Sounds like a joke... but I'm totally serious. I used to use the stuff for building models. That should give you plenty of workability in sanding down the clear coat without risk of dipping down into the stain. Granted, I haven't finished wood in a long time, so this might just be a crackpot idea. Good luck to you either way. I've been keeping an eye on this thread for the last couple months, and I'll be anxiously awaiting the final results of this awesome build.