This may or may not help but here goes.
I just changed out some cataract counterbalanced handles to wood.
Their counterweights are 1 1/4"x10 1/4" steel round bar.
Half of the counterweight is handle and the other half is cast into plastic the same ID as the shaft.
That is then glued into the shaft.
I used a heat gun to warm up the shaft to break the bond of the glue and used a strap wrench to twist it out of the shaft.
This can easily ruin the handle, I did.
I have also cut them down from the blade end and rebored the blade hole with a sharp unibit with a light touch.
This may be the way to go in this case.
Don't try to use twist bits to bore the hole, as it will splinter to much.
I think you would get the cleanest hole with a annular cutter, but I did not have one of the right diameter, so I don't know for certain.
One more thought is cut them to 9'-6" first then go to 9' if needed.
Easy to cut down, hard to add on to.