Ed,
I have a suggestion by what I've used to repair seams. Use silica, it's about $10 a bag, mixed with epoxy and inject it with a cheap syringe (Target gave me some for free at the pharmacy) to rejoin the halves then once it's dry fill in the top with micro balloons and epoxy so it will sand easier...just an idea. Milled fibers work great but it's easier to use the silica in a syringe.
Tim