Ridiculous amounts of time, alternating heat and solvent, and a total of three old clutch cables chucked up in a drill, fed in to it. The clutch arm end will go in the chuck, and with a bit of assistance from bolt cutters the pedal end will too...
Wear heavy gloves, the cable bits are sharp and the friction heats it up quite hot to hold.
If I had to do it again (and I did on the other one) I would start with heat and the cable and I'd skip the solvent. Penetrating oil did not seem to help either, but holding it vertical and ringing the flanges with a hammer every once in awhile helped to clear the accumulated debris. You'll be shocked how much carbon and rust will come out of that little tube.
Plan on about 10 hours each, if you have a dual port I think you can still buy them new, it would be a steal at any reasonable price if you value your time.
Steve