Thanks John and Jon. Well, I've been away so long I'm messing up on terminology. I was thinking more about separation in terms 'balance' as John pointed out. I'm thinking I might map out a frequency range for each instrument and put high and low shelves on either side.
Anyway, yes this was fun to do. If I can take a little pride I'm particularly pleased with the way the trombone parts came out. I only started learning how to play with a tremolo bar recently, and, after some practice, it worked well to mimic the trombone slides.
Oh, and Jon, much to my surprise listening to the original, it is in stereo with several instruments that sound hard-panned left or right. Hmmm, now that you all got me thinking about it I could try that. I'm not usually a fan of hard panning, but, as the saying goes "A foolish consistency is the hobgoblin of small minds."