I filled the cracks using a "mahogany" colored timber filler from StewMac - ended up a bit darker than ideal, but it works 'cos the 'burst means that area is deeper (and richer) colors anyway - it's holding well. I've been gently sanding the binding down each time, after watching DB say "don't bother masking the binding" so I didn't… I'm almost tempted to shoot for an aged, slightly yellow tone for the binding anyway to pick out the golden tones in the middle of the 'burst… I was actually planning to leave the headstock in its current shape versus going for a pseudo-Gibson look - I kinda like the shape of the raw blank.
Thanks all for feedback - really appreciate it - the bike handlebars was the best I could come up with, but it's been working pretty well overall.
Tomorrow I'll do another (I think final) color coat, then after that it'll be time for the top coat.